Alexei Navalny, the Russian opposition figure currently being held in a prison camp, has complained of a further deterioration in his health.
He has been diagnosed with a fever and a “severe cough”, but he will continue his hunger strike, which he started a few days ago, dpa news agency quoted Navalny as saying in an Instagram post on Monday.
Three of his fellow prisoners had already been taken to hospital because of tuberculosis.
According to the Izvestia newspaper on Monday evening, Navalny received medical care.
The 44-year-old was to be examined for signs of respiratory illness and elevated body temperature.
Navalny is “under the supervision of medical staff”, prison authorities said, according to the report.
A coronavirus test has also been carried out.
The leading opposition figure, who is imprisoned in the prison camp about 100 km east of Moscow, has been reporting severe back pain and paralysis in one leg for some time.
On March 31, Navalny declared that he had gone on hunger strike in protest at a lack of medical care.
In February, Navalny was sentenced to several years in prison.
The Russian judiciary accuses him of violating reporting requirements in an earlier criminal case while he was recovering in Germany from an assassination attempt involving the nerve agent Novichok.
According to a survey by independent pollsters Levada, just under a third of Russians, or 29 per cent, consider the verdict “rather unfair”.
Significantly more respondents, or 48 per cent, on the other hand, thought that Navalny’s conviction was probably justified.
Last August, Navalny fell into a coma after collapsing during a domestic flight.
He was treated for weeks at the Charite hospital in Berlin.
The prominent opposition figure blames a “hit squad” of the FSB domestic intelligence service, under the command of President Vladimir Putin, for the attempt on his life.
Putin and the FSB reject the accusations.