The 42-year-old Kremlin opponent was arrested in Crimea after Moscow's 2014 annexation of the peninsula.
PIC: Ukrainian film-maker Oleg Sentsov's cousin Natalya Kaplan (L) takes part in a rally in front of Russia embassy with an appeal to free Ukrainian film director Oleg Sentsov in Kiev on Wednesday. (AFP)
Western governments and activists on Tuesday stepped up pressure on Russia to free jailed Ukrainian filmmaker Oleg Sentsov as he reached day 100 of a hunger strike.
Ten protesters were also arrested by Russian police in Moscow on Tuesday in a demonstration to show support for Sentsov, according to the independent monitor OVD-Info.
The 42-year-old Kremlin opponent was arrested in Crimea after Moscow's 2014 annexation of the peninsula and has been languishing in a Russian Artic prison with little hope of release.
He announced the hunger strike in May demanding the release of all Ukrainian political prisoners being held in Russia.
Sentsov's cousin Natalia Kaplan was among several dozen people demonstrating in front of the Russian embassy in Kiev Tuesday.
Sentsov "does not intend to give up his strike, nor ask (Russian President Vladimir) Putin to pardon him," she told protesters, some of whom were carrying signs that read "Free Sentsov" and "Stop Putin".
"Oleg is hanging in there... He is not broken," she added.
But in an interview with AFP last week, Kaplan painted a gloomy picture of her relative's health and state of mind.
"He wrote to me that we mustn't tell him any more that freedom is coming. He doesn't believe it any more," she said.
"He has a very weak heartbeat of 40 beats per minute. He complains that his heart hurts, that he's weak, and he tries to not get up too often to preserve his strength."
'Could die any minute'
In the Czech Republic, filmmakers said they were launching a rotating hunger strike in solidarity with the director.
The French newspaper Le Monde carried a plea signed by dozens of figures from the world of culture calling for his release, saying "Oleg Sentsov could die any minute".
Ukrainian foreign ministry spokeswoman Mariana Betsa also demanded that Sentsov be freed.
"We call on our partners and international organisations to increase pressure on Russia to #SaveOlegSentsov and free Ukrainian political prisoners in Russia," she wrote on Twitter.
The father of two is receiving supplements in a drip usually meant for people who are unable to eat.
Russian rights ombudswoman Tatiana Moskalkova said doctors had found that Sentsov's condition was "satisfactory", adding "he moves, gets up, and gets a special diet".
She also said Sentsov could not be part of a prisoner-swap with Ukraine because he was automatically given Russian nationality when Crimea was annexed.
"We must look for a new legal way" for such an exchange, she said.
Vice speaker of the Ukrainian parliament Iryna Gerashchenko called the statements a "farce" and "blackmail", saying the only thing needed to free Sentsov was "Putin's political will".
Sentsov was convicted of planning arson attacks on pro-Moscow party offices in Crimea after Russia annexed the peninsula from Ukraine in 2014.
He had also taken part in the Maidan protests in Kiev during the winter of 2013-2014 that culminated in Moscow-backed president Viktor Yanukovych fleeing the country.
Sentsov was sentenced to 20 years imprisonment for terrorism and arms trafficking after a trial denounced as "Stalinist" by Amnesty International and criticised by Kiev, the EU and the US.
US State Department spokeswoman Heather Nauert on Tuesday said the US was "deeply concerned" by Sentsov's deteriorating health, adding: "We renew our demand that Russia immediately release him and all Ukrainian citizens unlawfully imprisoned in Russia and on the Crimean peninsula."
"His conviction on charges of plotting terrorist acts is widely regarded to be without merit and a cynical reprisal for his opposition to Russia's occupation of Crimea."
British junior foreign minister Alan Duncan said Tuesday the charges against Sentsov had been "fabricated," adding: "No one should be imprisoned for opposing the illegal annexation of Crimea."
Journalist and activist Zoya Svetova said the prisoner told her during a visit last week he had lost 17 kilograms (38 pounds), while prison medics said he had lost 11.
Sentsov was working on his second film when he was arrested. His first film "Gamer" is about a young video game player, and was shown at several European festivals in 2012.
G7 ambassadors as well as major figures from the world of cinema, from director Jean-Luc Godard to Hollywood star Johnny Depp, have previously called for Sentsov's release.
The Kremlin has so far remained unresponsive to requests for him to be freed, saying that a request for a pardon can only be filed by the prisoner himself, which Sentsov has refused to do.
In a rare public intervention on the subject in early June, Putin showed little sympathy towards Sentsov's plight.
Sentsov was arrested because "he was planning a terrorist attack" rather than because of opposition or artistic activities, the Russian president said.