MOSCOW (AP) — A Ukrainian filmmaker on hunger strike in a Russian prison has become increasingly frail and his condition has worsened considerably, his lawyer and his sister said.

Wednesday marks the 87th day that Oleg Sentsov has been refusing food. Sentsov is demanding that he and 64 other Ukrainians imprisoned in Russia whom he calls political prisoners be released.

His lawyer Dmitry Dinze said after visiting him Tuesday that Sentsov has a very low hemoglobin level, resulting in anemia and a slow heartbeat.

Dinze added that Sentsov refused to be moved to a civilian hospital, saying that a doctor there had threatened to tie him to a bed and force-feed him.

Sentsov's sister, Natalya Kaplan, said on Facebook after receiving a letter from him that his condition is "catastrophically bad" and he can barely raise himself from the bed.

"He wrote that the end is near, and he doesn't mean his release," Kaplan said.

She added that her brother also wrote to her that he wasn't getting any letters and found himself in an "information vacuum."

Sentsov is an opponent of Russia's 2014 annexation of Crimea and he was sentenced in 2015 to 20 years for conspiracy to commit terrorism, charges he denies. He has refused to seek a pardon from Russian President Vladimir Putin.

Western nations have campaigned for his release. Last month, the European Court of Human Rights urged Sentsov to end his hunger strike.