MOSCOW — Jailed Kremlin critic Alexei Navalny has been moved to a prison sick ward with symptoms of a respiratory illness, alarming supporters, who say he is being denied proper medical care and is being "slowly killed."

Navalny, 44, was tested for the coronavirus Monday after exhibiting symptoms of a respiratory illness, the federal prison service told Izvestia, a pro-Kremlin newspaper. Earlier, in an Instagram post under his name, Navalny said he had a high temperature and a cough, adding that three people from his prison ward had been hospitalized with tuberculosis.

Navalny declared a hunger strike last week, demanding proper medical care for his severe back pain and leg numbness. Navalny’s attorney, Olga Mikhailova, told the independent Dozhd TV on Monday that he has lost 13 kilograms (nearly 29 pounds) in three weeks.

Navalny joked darkly on Instagram: “If I have tuberculosis, then maybe it will banish back pain and numbness in my legs. That would be great.”

“I continue my hunger strike, of course,” he added. “I have a right guaranteed by law to invite a specialist doctor at my own expense. I will not give it up, and prison doctors can be trusted just as much as state TV.”

Yulia Navalnaya, Navalny’s wife, shared a letter Tuesday on Instagram from the director of the prison where Navalny is being held. In it, Alexander Mukhanov writes that the prison administration isn’t in possession of Navalny’s passport, so he cannot be hospitalized in case of illness.

Navalny survived poisoning from a nerve agent in August in what he has said was an assassination attempt ordered by President Vladimir Putin. After recovering in Germany for five months, Navalny was jailed immediately upon returning to Russia in January.

He was later sentenced to 2½ years in prison for breaching parole conditions in a 2014 fraud case, partly because he failed to report to authorities while under treatment in Germany.

On Friday, 30 human rights defenders signed a letter to Russia’s human rights commissioner, Tatyana Moskalkova, asking her to visit Navalny in the penal colony because “one gets the impression that he is being slowly killed there.”

A handful of Navalny’s supporters, including Anastasia Vasilyeva, head of Navalny-affiliated Alliance of Doctors, protested Tuesday outside the penal colony in Pokrov, about 60 miles east of Moscow. Vasilyeva demanded access to Navalny to examine him but was rebuffed. She and several others, including some journalists, were later detained.

Last week, Maria Butina, who was imprisoned in the United States after pleading guilty in 2018 to conspiring to act as an unregistered foreign agent of Russia, visited Navalny’s prison ward with a camera crew from the Kremlin-funded RT television network, formerly Russia Today. She wrote on social media: “I’m tired of the complaining. He is in one of the best penal colonies in Russia.”

In an Instagram post March 26, Navalny wrote that Mikhail Khodorkovsky, a prominent Russian opposition figure who spent 10 years in a penal colony, warned him: “The main thing is not to get sick there. Nobody will be treating you. If you get seriously ill, you will die.”

Mary Ilyushina contributed to this report.