“We urge Russian authorities to unconditionally release him as a matter of urgency,” the UN experts declared.

Oleg Sentsov was arrested by Russian authorities in May 2014 in Crimea, and convicted to 20 years in a Russian prison, as a Russian citizen, on charges of terrorism. The Ukrainian peninsula of Crimea was annexed by Russia earlier that year, in contravention of international law.

In March 2014, the UN General Assembly adopted a resolution calling on States not to recognize changes in status of the Crimea, and last September, a report from the UN human rights office (OHCHR) said that rights had significantly deteriorated under Russian occupation, including arbitrary arrests and detentions, enforced disappearances, ill-treatment and torture. 

Mr Sentsov went on hunger strike three months ago, to protest what he believes is the politically-motivated incarceration of 64 Ukrainians in Russian prisons.

They also called on the Russian authorities to ensure that Mr. Sentsov is immediately provided with appropriate medical treatment, based on his full and informed consent.The rights experts expressed grave concern for his physical and mental integrity. “Sentsov’s life is in imminent danger. His hunger strike follows a trial and a conviction that has fallen short of international law,” the experts said.

According news reports, his mother had written to Russian President Vladimir Putin at the end of June pleading for her son's release, but was told that pardons would only be considered if the prisoner made the request, which Mr Sentsov has refused to do.

The UN human rights experts – David Kaye, UN Special Rapporteur on the promotion and protection of the right to freedom of opinion and expression; Dainius Pūras, Special Rapporteur on the right to physical and mental health; and Michel Forst, Special Rapporteur on the situation of human rights defenders – remain in contact with the Russian authorities about this case.

Special Rapporteurs and independent experts are appointed by the Geneva-based UN Human Rights Council to examine and report back on a specific human rights theme or a country situation. The positions are honorary and the experts are not UN staff, nor are they paid for their work.