MOSCOW — Doctors for jailed Russian opposition leader Alexei Navalny appealed Thursday for him to end his more than three-week hunger strike after prison authorities allowed civilian physicians to examine him.

In a letter from five physicians affiliated with Navalny, published by Russia’s independent Mediazona news outlet, they said Navalny was examined at a civilian hospital Tuesday, according to his lawyers. Navalny started his hunger strike three weeks ago as a demand to see independent specialists of his choosing at his expense.

Russia’s treatment of Navalny has drawn international condemnation, including from the United States, which promised “consequences” for the Kremlin if Navalny were to die in prison. His condition, described as being near death by his allies, prompted mass protests throughout Russia on Wednesday.

“Our main task is to preserve our patient's life and health,” the letter from the five doctors said. “Thus, we, as attending physicians, appeal to Alexei Navalny and ask him to immediately stop the hunger strike in order to preserve his life and health. We consider the fact that civilian doctors were allowed to see him and conduct independent examinations and consultations to be sufficient for this.”

“We understand that if the hunger strike continues even for a minimal time, unfortunately, we will soon have no one to heal,” it added.

Yaroslav Ashikhmin, Navalny’s personal physician and one of the doctors who signed the letter, wrote on Facebook last week that blood tests on Navalny revealing high potassium were indicative of kidney failure and that severe heart-rhythm disturbances threatened cardiac arrest.

Navalny, who is serving a more-than two-year prison sentence, was then moved to a prison hospital at a different location on Sunday.

But his allies continued to be critical of his medical care, especially that his team of physicians had not been allowed to examine him. His attorneys previously said Navalny, 44, has two herniated discs that have caused extreme back pain and numbness in his leg and hands.

He was poisoned with a nerve-agent in August — a hit he and Western intelligence agencies say was carried out by Russian state security agents — and though Navalny returned to Russia after a five-month recovery in Germany, there could be lingering effects on his health.

Navalny’s doctors said that his consultations at a hospital in Russia’s Vladimir region on Tuesday involved a neurosurgeon, neurologist and nephrologist. His lawyers and relatives handed over the test results to his personal doctors on Thursday, asking for their opinion.

“Of course, we continue to insist on the realization of the patient's right to receive our opinion in person,” Navalny’s doctors said in the letter. “We believe that as independent doctors, we can also take part in the consultations, if necessary, since there is a sufficient amount of data on the patient's life and medical history that could be useful to our colleagues who are supervising him at the moment.”