* Lawyers unable to see Navalny in prison

* Allies are worried about his health

* Prison service says his health is satisfactory

* Cultural figures make public appeal (Adds Kremlin, public appeal to authorities from cultural figures)

By Andrew Osborn and Gabrielle Tétrault-Farber

His supporters said a day earlier they were concerned by a deterioration in his health and his lawyers said they had not been allowed to visit him in prison. They returned on Thursday to try to see him.

Leonid Volkov, a close Navalny ally, has said that Navalny began to experience serious back pain last week, had felt a numbness in his leg and been unable to stand on it. He was given two Ibuprofen pills for the pain, Volkov said.

The Federal Penitentiary Service said earlier on Thursday that the 44-year-old opposition politician’s health was stable and satisfactory.

It said prisons in the Vladimir region, where Navalny is being held, had carried out medical examinations on inmates on Wednesday. The checks had been conducted at inmates’ request, it said, and Navalny had been examined, too.

“His health is deemed stable and satisfactory, according to the results of the examination,” the penitentiary service said, according to the Interfax news agency.

‘REALLY WORRIED’

The statement did not satisfy Navalny‘s allies.

“Now we are really worried,” Navalny’s Anti-Corruption Foundation wrote on Twitter. “Even the Federal Penitentiary Service can’t call Navalny’s condition `good’.”

Nearly 160 cultural figures, including writers, musicians and film directors, published an open letter to the authorities on Thursday demanding Navalny‘s lawyers be given access to him and that he be held in normal conditions.

They said they had “serious grounds to be concerned about his health and life”.

In particular, they demanded that the practice of waking him up every hour during the night due to his classification as a flight risk be ended.

The Kremlin said it was not following developments with Navalny‘s health, which it said was a matter for prison authorities.

Navalny was jailed last month for two and a half years on charges he called politically motivated. He was arrested as he returned to Russia from Germany in January, where he had been recovering from what doctors said was a nerve agent poisoning.

The West, including the European Court of Human Rights, has demanded Russia release Navalny. Moscow dismissed the court’s ruling as “unlawful” and has called similar appeals unacceptable interference in its internal affairs.

Navalny‘s allies on Tuesday announced plans to stage what they hope will be the biggest anti-Kremlin street protest in modern Russian history this spring, in a bid to have him released. The authorities have said such protests are illegal. (Additional reporting by Anton Kolodyazhnyy and Polina Nikolskaya; editing by Gareth Jones, Larry King)