Sentsov, 42, is serving a 20-year-sentence in a Siberian prison on terrorism charges after being convicted three years ago of arson in his native Crimea following its annexation by Moscow.

The imprisonment and case surrounding Sentsov has been widely reported in France, where the director enjoys wide support.

Figure of opposition to the annexation of Crimea

"Today, a filmmaker is dying because he is a dissident," said an open letter published in the French newspaper Le Monde and signed by around 120 actors and directors, joined by French Culture Minister Françoise Nyssen. The letter compared his plight to that of dissident novelist Alexander Solzhenitsyn, who spent seven years in a Soviet gulag.

French President Emmanuel Macron called Russian President Vladimir Putin on Friday to petition for the release of Sentsov. According to a statement issued by the Elysée Palace, Macron made "several proposals" to bring about a solution and Putin pledged to respond quickly.

Anastasiya Shapochkina, a specialist on European Union relations with Russia at Paris’ Sciences Po University, told FRANCE 24, “Macron has been under pressure for months from the French media, world of culture and human rights organisations to take action for Sentsov."

Shapochkina further said that Macron “does not want to have his [Senstov’s] death on his conscience… he would face severe criticism”.

Health deteriorating

Last week Sentsov's cousin, Natalia Kaplan, warned that his health was "catastrophically bad".

His lawyer said Friday he was "ready to die" but Russian authorities have consistently played down fears over his health.

In a statement on Saturday, the prison service said he was "not seen to be underweight and a worsening in his state of health is not observed".

It added that it was "taking all the necessary measures", including giving him nutritional supplements to protect his health, which it described as "satisfactory".

Sentsov himself has refused to be taken to hospital.

(FRANCE 24 with AFP)