Crimean native Sentsov announced a hunger strike demanding the release of Ukrainian political prisoners on May 14 while serving a 20-year prison sentence on a terrorism conviction. More than 200,000 people have signed a petition seeking to secure Sentsov’s release, while the Kremlin has rejected several requests to pardon him.

As jailed Ukrainian filmmaker Oleg Sentsov enters day 100 of his hunger strike in a Russian prison, his colleagues and activists around the world have raised the alarm over his rapidly deteriorating health.

“I don’t think he can hold himself for many more days. Crisis can set in at any time,” Zoya Svetova, a human rights activist who recently visited Sentsov at his prison colony in northern Russia, told The Moscow Times on Tuesday.

The activist said that Russian authorities have ignored proposals to swap the vocal critic of Moscow’s 2014 annexation of Crimea for Russians held in Ukraine.

“All we can do is hope that something is happening behind closed doors. If not, then Russia has decided that Sentsov has died and will let him die,” she said.

Several Russian and Ukrainian cities scheduled events on Tuesday to mark the 100th day of Sentsov’s hunger strike, the U.S.-funded Radio Svoboda reported.

A protest is also scheduled in central Moscow later on Tuesday, with its author calling on participants to demand the Crimean film director’s release alongside what he called other political prisoners in Russia.

In the Czech Republic, five filmmakers will reportedly take turns fasting for a day in a show of solidarity with Sentsov starting Tuesday.

“PEN members will deliver messages of support from all over the world to the Russian Embassy [in London], urging the authorities to ensure that Sentsov is allowed to receive them,” the PEN International writers’ association said on Facebook announcing the commemoration.

The Public Monitoring Commission (PMC) prison watchdog told Interfax that prison authorities follow protocol where they force-feed a prisoner if his life is threatened.

In a handwritten Aug. 14 letter posted on the Change.org petition, Sentsov told supporters “I’ll try to not let you all down, give up or die.”

“Although only two of these three wishes could be fulfilled for sure,” he wrote, adding a smiley face.