Free-expression group PEN America called on US President Donald Trump to raise the fate of a hunger-striking Ukrainian filmmaker at a summit Monday with his Russian counterpart Vladimir Putin.
Oleg Sentsov -- arguably Russia's most prominent prisoner -- has refused food for 63 days in a bid to win the release of Ukrainian political prisoners held in Russia.
He is serving a 20-year sentence after being convicted on terrorism charges over an alleged arson plot in Crimea. His supporters say the case was trumped up.
But the Kremlin has shown no sign of being ready to cave in to his demand and hopes are fading that the Ukrainian filmmaker and activist will make it out of his Russian prison alive.
"The world needs leadership to strengthen democracy and the rule of law," PEN America's Washington director Tom Melia said, urging Trump to discuss Sentsov's fate with Putin.
At a demonstration in Helsinki, Sentsov's cousin Natalya Kaplan, speaking alongside PEN America activists, reminded the crowd that the filmmaker's mother had asked Putin to pardon him.
Kaplan urged them to "make sure that he hears this message and responds," the free speech advocacy group quoted her as saying in a statement.
Western governments led by French President Emmanuel Macron and celebrities including Pedro Almodovar, Johnny Depp and Stephen King have repeatedly urged the Kremlin to release Sentsov. Renowned Russian filmmaker Alexander Sokurov asked Pope Francis to intervene.
Last week supporters released an appeal by Sentsov's mother Lyudmila to Putin. She said his two children -- including an autistic son -- needed him to come home.
Sentsov, 42, launched his hunger strike on May 14 to demand Russia release Ukrainian political prisoners.
He is being sustained with water and a glucose drip and has lost around 15 kilogrammes in weight, his relatives say.
On average, humans can survive without food for about two months.
The vocal Kremlin critic was detained in Crimea in 2014 after Russia annexed the Black Sea peninsula from Ukraine.
Supporters say Russia wanted to make an example of him with a particularly harsh sentence for masterminding arson attacks, which he denies.