TOPSHOT - A Russian police officer patrols outside the territory of the penal colony N2, where Kremlin critic Alexei Navalny has been transferred to serve a two-and-a-half year prison term for violating parole, in the town of Pokrov on April 6, 2021. - The Alliance of Doctors medical trade union said it would organise a protest outside the penal colony in Pokrov on Tuesday, demanding Navalny receive adequate medical treatment. (Photo by Kirill KUDRYAVTSEV / AFP)

Police officers wearing face masks to protect against coronavirus guard an entrance of the prison colony IK-2, which stands out among Russian penitentiary facilities for its particularly strict regime, in Pokrov in the Vladimir region, 85 kilometers (53 miles) east of Moscow, Russia, Tuesday, April 6, 2021. Doctors from the Navalny-backed Alliance of Doctors announced going to the Pokrov prison on Tuesday to demand the opposition leader gets qualified medical help from independent doctors after he complained about pain in his leg and back.(AP Photo/Pavel Golovkin)

Police officers wearing face masks to protect against coronavirus guard an entrance of the prison colony IK-2, which stands out among Russian penitentiary facilities for its particularly strict regime, in Pokrov in the Vladimir region, 85 kilometers (53 miles) east of Moscow, Russia, Tuesday, April 6, 2021. Doctors from the Navalny-backed Alliance of Doctors announced going to the Pokrov prison on Tuesday to demand the opposition leader gets qualified medical help from independent doctors after he complained about pain in his leg and back.(AP Photo/Pavel Golovkin)

Police officers wearing face masks to protect against coronavirus guard an entrance of the prison colony IK-2, which stands out among Russian penitentiary facilities for its particularly strict regime, in Pokrov in the Vladimir region, 85 kilometers (53 miles) east of Moscow, Russia, Tuesday, April 6, 2021. Doctors from the Navalny-backed Alliance of Doctors announced going to the Pokrov prison on Tuesday to demand the opposition leader gets qualified medical help from independent doctors after he complained about pain in his leg and back.(AP Photo/Pavel Golovkin)

The Alliance of Doctors union's leader Anastasia Vasilyeva, center in white arrives to the prison colony IK-2, which stands out among Russian penitentiary facilities for its particularly strict regime, in Pokrov in the Vladimir region, 85 kilometers (53 miles) east of Moscow, Russia, Tuesday, April 6, 2021. Doctors from the Navalny-backed Alliance of Doctors announced going to the Pokrov prison on Tuesday to demand the opposition leader gets qualified medical help from independent doctors after he complained about pain in his leg and back. (AP Photo/Pavel Golovkin)

The Alliance of Doctors union's leader Anastasia Vasilyeva, center, gestures while speaking to police at the prison colony IK-2, which stands out among Russian penitentiary facilities for its particularly strict regime, in Pokrov in the Vladimir region, 85 kilometers (53 miles) east of Moscow, Russia, Tuesday, April 6, 2021. Doctors from the Navalny-backed Alliance of Doctors announced going to the Pokrov prison on Tuesday to demand the opposition leader gets qualified medical help from independent doctors after he complained about pain in his leg and back. (AP Photo/Pavel Golovkin)

The Alliance of Doctors union's leader Anastasia Vasilyeva, center, stands next to police officers at the prison colony IK-2, which stands out among Russian penitentiary facilities for its particularly strict regime, in Pokrov in the Vladimir region, 85 kilometers (53 miles) east of Moscow, Russia, Tuesday, April 6, 2021. Doctors from the Navalny-backed Alliance of Doctors announced going to the Pokrov prison on Tuesday to demand the opposition leader gets qualified medical help from independent doctors after he complained about pain in his leg and back. (AP Photo/Pavel Golovkin)

The Alliance of Doctors union's leader Anastasia Vasilyeva, left, stands to police at the prison colony IK-2, which stands out among Russian penitentiary facilities for its particularly strict regime, in Pokrov in the Vladimir region, 85 kilometers (53 miles) east of Moscow, Russia, Tuesday, April 6, 2021. Doctors from the Navalny-backed Alliance of Doctors announced going to the Pokrov prison on Tuesday to demand the opposition leader gets qualified medical help from independent doctors after he complained about pain in his leg and back. (AP Photo/Pavel Golovkin)

The Alliance of Doctors union's leader Anastasia Vasilyeva, left, speaks to the media at the prison colony IK-2, which stands out among Russian penitentiary facilities for its particularly strict regime, in Pokrov in the Vladimir region, 85 kilometers (53 miles) east of Moscow, Russia, Tuesday, April 6, 2021. Doctors from the Navalny-backed Alliance of Doctors announced going to the Pokrov prison on Tuesday to demand the opposition leader gets qualified medical help from independent doctors after he complained about pain in his leg and back. (AP Photo/Pavel Golovkin)

The Alliance of Doctors union's leader Anastasia Vasilyeva, center in white, arrives to the prison colony IK-2, which stands out among Russian penitentiary facilities for its particularly strict regime, in Pokrov in the Vladimir region, 85 kilometers (53 miles) east of Moscow, Russia, Tuesday, April 6, 2021. Doctors from the Navalny-backed Alliance of Doctors announced going to the Pokrov prison on Tuesday to demand the opposition leader gets qualified medical help from independent doctors after he complained about pain in his leg and back. (AP Photo/Pavel Golovkin)

The Alliance of Doctors union's leader Anastasia Vasilyeva, right, speaks to the media at the prison colony IK-2, which stands out among Russian penitentiary facilities for its particularly strict regime, in Pokrov in the Vladimir region, 85 kilometers (53 miles) east of Moscow, Russia, Tuesday, April 6, 2021. Doctors from the Navalny-backed Alliance of Doctors announced going to the Pokrov prison on Tuesday to demand the opposition leader gets qualified medical help from independent doctors after he complained about pain in his leg and back. (AP Photo/Pavel Golovkin)

The Alliance of Doctors union's leader Anastasia Vasilyeva speaks to the media at the prison colony IK-2, which stands out among Russian penitentiary facilities for its particularly strict regime, in Pokrov in the Vladimir region, 85 kilometers (53 miles) east of Moscow, Russia, Tuesday, April 6, 2021. Doctors from the Navalny-backed Alliance of Doctors announced going to the Pokrov prison on Tuesday to demand the opposition leader gets qualified medical help from independent doctors after he complained about pain in his leg and back. (AP Photo/Pavel Golovkin)

Police officers film as the Alliance of Doctors union's leader Anastasia Vasilyeva speaks to the media at the prison colony IK-2, which stands out among Russian penitentiary facilities for its particularly strict regime, in Pokrov in the Vladimir region, 85 kilometers (53 miles) east of Moscow, Russia, Tuesday, April 6, 2021. Doctors from the Navalny-backed Alliance of Doctors announced going to the Pokrov prison on Tuesday to demand the opposition leader gets qualified medical help from independent doctors after he complained about pain in his leg and back. (AP Photo/Denis Kaminev)

Police officers detain the Alliance of Doctors union's leader Anastasia Vasilyeva at the prison colony IK-2, which stands out among Russian penitentiary facilities for its particularly strict regime, in Pokrov in the Vladimir region, 85 kilometers (53 miles) east of Moscow, Russia, Tuesday, April 6, 2021. Doctors from the Navalny-backed Alliance of Doctors announced going to the Pokrov prison on Tuesday to demand the opposition leader gets qualified medical help from independent doctors after he complained about pain in his leg and back. (AP Photo/Pavel Golovkin)

Police officer detain the Alliance of Doctors union's leader Anastasia Vasilyeva at the prison colony IK-2, which stands out among Russian penitentiary facilities for its particularly strict regime, in Pokrov in the Vladimir region, 85 kilometers (53 miles) east of Moscow, Russia, Tuesday, April 6, 2021. Doctors from the Navalny-backed Alliance of Doctors announced going to the Pokrov prison on Tuesday to demand the opposition leader gets qualified medical help from independent doctors after he complained about pain in his leg and back. (AP Photo/Pavel Golovkin)

Police officers detain the Alliance of Doctors union's leader Anastasia Vasilyeva at the prison colony IK-2, which stands out among Russian penitentiary facilities for its particularly strict regime, in Pokrov in the Vladimir region, 85 kilometers (53 miles) east of Moscow, Russia, Tuesday, April 6, 2021. Doctors from the Navalny-backed Alliance of Doctors announced going to the Pokrov prison on Tuesday to demand the opposition leader gets qualified medical help from independent doctors after he complained about pain in his leg and back. (AP Photo/Pavel Golovkin)

Police officers detain the Alliance of Doctors union's leader Anastasia Vasilyeva at the prison colony IK-2, which stands out among Russian penitentiary facilities for its particularly strict regime, in Pokrov in the Vladimir region, 85 kilometers (53 miles) east of Moscow, Russia, Tuesday, April 6, 2021. Doctors from the Navalny-backed Alliance of Doctors announced going to the Pokrov prison on Tuesday to demand the opposition leader gets qualified medical help from independent doctors after he complained about pain in his leg and back. (AP Photo/Pavel Golovkin)

Police officers detain the Alliance of Doctors union's leader Anastasia Vasilyeva at the prison colony IK-2, which stands out among Russian penitentiary facilities for its particularly strict regime, in Pokrov in the Vladimir region, 85 kilometers (53 miles) east of Moscow, Russia, Tuesday, April 6, 2021. Doctors from the Navalny-backed Alliance of Doctors announced going to the Pokrov prison on Tuesday to demand the opposition leader gets qualified medical help from independent doctors after he complained about pain in his leg and back. (AP Photo/Pavel Golovkin)

Activist Ksenia Pakhomova, foreground, takes a selfie as police officers detain her at the prison colony IK-2, which stands out among Russian penitentiary facilities for its particularly strict regime, in Pokrov in the Vladimir region, 85 kilometers (53 miles) east of Moscow, Russia, Tuesday, April 6, 2021. Doctors from the Navalny-backed Alliance of Doctors announced going to the Pokrov prison on Tuesday to demand the opposition leader gets qualified medical help from independent doctors after he complained about pain in his leg and back. (AP Photo/Pavel Golovkin)

Matthew Chance, CNN Senior International Correspondent in Moscow gestures as police officers detain him at the prison colony IK-2, which stands out among Russian penitentiary facilities for its particularly strict regime, in Pokrov in the Vladimir region, 85 kilometers (53 miles) east of Moscow, Russia, Tuesday, April 6, 2021. Doctors from the Navalny-backed Alliance of Doctors announced going to the Pokrov prison on Tuesday to demand the opposition leader gets qualified medical help from independent doctors after he complained about pain in his leg and back. (AP Photo/Pavel Golovkin)

Police officers wearing face masks to protect against coronavirus guard an entrance of the prison colony IK-2, which stands out among Russian penitentiary facilities for its particularly strict regime, with the sign reads "Security zone", in Pokrov in the Vladimir region, 85 kilometers (53 miles) east of Moscow, Russia, Tuesday, April 6, 2021. Doctors from the Navalny-backed Alliance of Doctors announced going to the Pokrov prison on Tuesday to demand the opposition leader gets qualified medical help from independent doctors after he complained about pain in his leg and back. (AP Photo/Denis Kaminev)

Russian police officers guard the entrance to the penal colony N2, where Kremlin critic Alexei Navalny has been transferred to serve a two-and-a-half year prison term for violating parole, in the town of Pokrov on April 6, 2021. - The Alliance of Doctors medical trade union said it would organise a protest outside the penal colony in Pokrov on Tuesday, demanding Navalny receive adequate medical treatment. (Photo by Kirill KUDRYAVTSEV / AFP)

Russian police officers guard the entrance to the penal colony N2, where Kremlin critic Alexei Navalny has been transferred to serve a two-and-a-half year prison term for violating parole, in the town of Pokrov on April 6, 2021. - The Alliance of Doctors medical trade union said it would organise a protest outside the penal colony in Pokrov on Tuesday, demanding Navalny receive adequate medical treatment. (Photo by Kirill KUDRYAVTSEV / AFP)

Russian police officers guard the entrance to the penal colony N2, where Kremlin critic Alexei Navalny has been transferred to serve a two-and-a-half year prison term for violating parole, in the town of Pokrov on April 6, 2021. - The Alliance of Doctors medical trade union said it would organise a protest outside the penal colony in Pokrov on Tuesday, demanding Navalny receive adequate medical treatment. (Photo by Kirill KUDRYAVTSEV / AFP)

A Russian police officer patrols outside the territory of the penal colony N2, where Kremlin critic Alexei Navalny has been transferred to serve a two-and-a-half year prison term for violating parole, in the town of Pokrov on April 6, 2021. - The Alliance of Doctors medical trade union said it would organise a protest outside the penal colony in Pokrov on Tuesday, demanding Navalny receive adequate medical treatment. (Photo by Kirill KUDRYAVTSEV / AFP)

Russian police officer patrols outside the territory of the penal colony N2 with an Orthodox church on the grounds where Kremlin critic Alexei Navalny has been transferred to serve a two-and-a-half year prison term for violating parole, in the town of Pokrov on April 6, 2021. - The Alliance of Doctors medical trade union said it would organise a protest outside the penal colony in Pokrov on Tuesday, demanding Navalny receive adequate medical treatment. (Photo by Kirill KUDRYAVTSEV / AFP)

Russian police officers guard the entrance to the penal colony N2, where Kremlin critic Alexei Navalny has been transferred to serve a two-and-a-half year prison term for violating parole, in the town of Pokrov on April 6, 2021. - The Alliance of Doctors medical trade union said it would organise a protest outside the penal colony in Pokrov on Tuesday, demanding Navalny to receive adequate medical treatment. (Photo by Kirill KUDRYAVTSEV / AFP)

Russian police officers guard the entrance to the penal colony N2, where Kremlin critic Alexei Navalny has been transferred to serve a two-and-a-half year prison term for violating parole, in the town of Pokrov on April 6, 2021. - The Alliance of Doctors medical trade union said it would organise a protest outside the penal colony in Pokrov on Tuesday, demanding Navalny to receive adequate medical treatment. (Photo by Kirill KUDRYAVTSEV / AFP)

Russian police officers guard the entrance to the penal colony N2, where Kremlin critic Alexei Navalny has been transferred to serve a two-and-a-half year prison term for violating parole, in the town of Pokrov on April 6, 2021. - The Alliance of Doctors medical trade union said it would organise a protest outside the penal colony in Pokrov on Tuesday, demanding Navalny to receive adequate medical treatment. (Photo by Kirill KUDRYAVTSEV / AFP)

Russian police handler wearing a face mask patrols the entrance to the penal colony N2, where Kremlin critic Alexei Navalny has been transferred to serve a two-and-a-half year prison term for violating parole, in the town of Pokrov on April 6, 2021. - The Alliance of Doctors medical trade union said it would organise a protest outside the penal colony in Pokrov on Tuesday, demanding Navalny receive adequate medical treatment. (Photo by Kirill KUDRYAVTSEV / AFP)

Russian police dog handler wearing a face mask patrols near the entrance to the penal colony N2, where Kremlin critic Alexei Navalny has been transferred to serve a two-and-a-half year prison term for violating parole, in the town of Pokrov on April 6, 2021. - The Alliance of Doctors medical trade union said it would organise a protest outside the penal colony in Pokrov on Tuesday, demanding Navalny receive adequate medical treatment. (Photo by Kirill KUDRYAVTSEV / AFP)

A Russian police officer wearing a face mask guards the entrance to the penal colony N2, where Kremlin critic Alexei Navalny has been transferred to serve a two-and-a-half year prison term for violating parole, in the town of Pokrov on April 6, 2021. - The Alliance of Doctors medical trade union said it would organise a protest outside the penal colony in Pokrov on Tuesday, demanding Navalny receive adequate medical treatment. (Photo by Kirill KUDRYAVTSEV / AFP)

Russian police officers wearing face masks guard the entrance to the penal colony N2, where Kremlin critic Alexei Navalny has been transferred to serve a two-and-a-half year prison term for violating parole, in the town of Pokrov on April 6, 2021. - The Alliance of Doctors medical trade union said it would organise a protest outside the penal colony in Pokrov on Tuesday, demanding Navalny receive adequate medical treatment. (Photo by Kirill KUDRYAVTSEV / AFP)

Russian police officers guard the entrance to the penal colony N2, where Kremlin critic Alexei Navalny has been transferred to serve a two-and-a-half year prison term for violating parole, in the town of Pokrov on April 6, 2021. - The Alliance of Doctors medical trade union said it would organise a protest outside the penal colony in Pokrov on Tuesday, demanding Navalny receive adequate medical treatment. (Photo by Kirill KUDRYAVTSEV / AFP)

Russian police officers wearing face masks film as they guard the entrance to the penal colony N2, where Kremlin critic Alexei Navalny has been transferred to serve a two-and-a-half year prison term for violating parole, in the town of Pokrov on April 6, 2021. - The Alliance of Doctors medical trade union said it would organise a protest outside the penal colony in Pokrov on Tuesday, demanding Navalny receive adequate medical treatment. (Photo by Kirill KUDRYAVTSEV / AFP)

Russian police officers wearing face masks film as they guard the entrance to the penal colony N2, where Kremlin critic Alexei Navalny has been transferred to serve a two-and-a-half year prison term for violating parole, in the town of Pokrov on April 6, 2021. - The Alliance of Doctors medical trade union said it would organise a protest outside the penal colony in Pokrov on Tuesday, demanding Navalny receive adequate medical treatment. (Photo by Kirill KUDRYAVTSEV / AFP)

Russian police handler wearing a face mask patrols near the entrance to the penal colony N2, where Kremlin critic Alexei Navalny has been transferred to serve a two-and-a-half year prison term for violating parole, in the town of Pokrov on April 6, 2021. - The Alliance of Doctors medical trade union said it would organise a protest outside the penal colony in Pokrov on Tuesday, demanding Navalny receive adequate medical treatment. (Photo by Kirill KUDRYAVTSEV / AFP)

Russian police officers guard the entrance to the penal colony N2, where Kremlin critic Alexei Navalny has been transferred to serve a two-and-a-half year prison term for violating parole, in the town of Pokrov on April 6, 2021. - The Alliance of Doctors medical trade union said it would organise a protest outside the penal colony in Pokrov on Tuesday, demanding Navalny to receive adequate medical treatment. (Photo by Kirill KUDRYAVTSEV / AFP)

Russian police officers guard the entrance to the penal colony N2, where Kremlin critic Alexei Navalny has been transferred to serve a two-and-a-half year prison term for violating parole, in the town of Pokrov on April 6, 2021. - The Alliance of Doctors medical trade union said it would organise a protest outside the penal colony in Pokrov on Tuesday, demanding Navalny to receive adequate medical treatment. (Photo by Kirill KUDRYAVTSEV / AFP)