Navalny, known as President Vladimir Putin’s fiercest critic, arrived in a penal colony about 60 miles east of Moscow earlier this month, where he has been sent to serve a two-and-a-half year prison sentence he received in a trial widely criticized as political.
Lawyers for Navalny have been trying for nearly two days to gain access to him at the Correctional Colony No. 2 prison.
The lawyers, Vadim Kobzev and Olga Mikhailova, said Thursday they had finally managed to meet with Navalny.
Kobzev said Navalny was suffering from severe back pain that was now making it difficult for him to walk and he was getting substantially worse because authorities were preventing him from getting treated.
The lawyers published two formal complaints that Navalny has filed with Russia’s Federal Penitentiary Service, in which he accuses prison authorities of deliberately denying him medical care and of subjecting him to sleep deprivation.
Navalny wrote that he has had “acute pain” in his back since late February when he was still in a detention center in Moscow, but that his requests to be examined by his own qualified doctor have been rejected. The pain has now spread, causing numbness in right leg, he said.
Navalny said he had been examined by a doctor last Friday but was never told of his diagnosis. The only treatment he had received so far was two tablets of ibuprofen.
"We’re seeing a classic picture of the development of an illness connected with a pinched nerve in the absence of appropriate treatment," Navalny wrote.
Navalny also said he is woken up hourly at night by guards shining a torch in his face to record he is still in his bed. He said the practice amounted to "torture by insomnia."
Navalny and his lawyers are demanding that he is given immediate access to his doctor and that the sleep deprivation stop.
"I’m not demanding that the administration of Correctional Colony No. 2 bake me a cake," Navalny wrote. "I am demanding to realize in full measure my right to receive medical care."
Russian authorities so far have denied that Navalny requires more medical care. Russia’s Federal Penitentiary Service earlier on Thursday announced it had conducted a medical examination of Navalny at the prison and that his health was "considered stable, satisfactory."
Navalny chose to return to Russia after narrowly surviving a nerve agent poisoning last summer and his family has suggested his health could still be suffering from it.
Navalny’s lawyers and his wife, Yulia Navalny, said Navalny until now had forbidden them to publicly talk about his back problem, not wanting to appear to be complaining.
“Everyone who knows Alexey knows that he won’t complain to the bitter end. He will put up with it, try to get by himself and to make jokes,” Yulia Navalny wrote on Instagram.
But she said she was now demanding her husband receive treatment from doctors he trust. Putin himself should release Navalny, she said.
"I demand the immediate freeing of my husband, Alexey Navalny, who he has locked in prison illegally. Locked him up because he’s afraid of political competition," she wrote.
The prison where Navalny is being held in the Vladimirskaya region is notorious among Russian prisoners for its strictness and for frequently blocking access to inmates’ lawyers and relatives. Prisoners spend much of the day on their feet and have virtually no free time, former inmates have told ABC News and other media.
Denying inmates adequate medical care is also routine in Russian prisons, according to human rights monitors. Prisoners can go weeks requesting medical examinations before seeing a doctor.
Navalny spent months recuperating in Germany following his poisoning that left him in a coma. Navalny, 41, had to relearn how to move, undergoing physical therapy, but he has appeared to recover well. His doctors, however, said the Novichok nerve agent could leave lingering nerve damage and other health problems.
Navalny’s team recently announced plans for a new street protest later this spring. Tens of thousands of people joined protests across Russia in late January after Navalny was arrested following his return to Moscow. But after two weeks of intense crackdown that saw thousands detained, Navalny's organizers called off any further street demonstrations, saying the movement needed to conserve its strength and that it would be irresponsible to continue when it was clear short-term demonstrations would not force the Kremlin to release Navalny.
The team said they were taking a different approach and would not name a date for the new protest until 500,000 people said they would attend by registering at a website created by Navalny's group. After more than two days, the website shows nearly 247,000 people have registered to take part in the protest.