MOSCOW (Reuters) - A Ukrainian film director jailed in Russia on what he says are political charges has promised to press on with a hunger strike that could end his life while Russia is hosting the soccer World Cup, which kicks off on Thursday.

FILE PHOTO: Ukrainian film director Oleg Sentsov gestures inside a defendants' cage as he attends a court hearing in Rostov-on-Don, Russia August 25, 2015. REUTERS/Sergey Pivovarov/File Photo

Oleg Sentsov, who has been on hunger strike since May 14, wants to highlight Russia’s human rights record at a time when it is in the global spotlight, and also to secure the release of other Ukrainians jailed in Russia. Sentsov views them too as political prisoners, a description Moscow rejects.

Human rights activists and Ukrainian politicians hope that President Vladimir Putin might release Sentsov and others as a good will gesture for the World Cup or as part of a prisoner swap with Kiev, something Putin has so far declined to do.

More than 50 writers and figures from the arts world, including novelists Salman Rushdie and Margaret Atwood, have written to Putin asking him to free Sentsov, who has said he is ready to die to bring attention to his case.

A Russian military court sentenced Sentsov to 20 years in a maximum security prison in 2015 after finding him guilty of setting fire to two offices in Crimea, including one belonging to Russia’s ruling political party, after Moscow annexed the territory from Ukraine.

Sentsov was also convicted of plotting to blow up a statue.

Sentsov, 41, pleaded not guilty at the time and denounced his trial as politically motivated. The European Union said the case was “in breach of international law” and the U.S. State Department called it a “clear miscarriage of justice”.

Sentsov, previously best known inside Ukraine for his 2011 film “Gamer”, is now best known for his opposition to Russia’s annexation of Crimea and for his defiant stance in jail.

“I AM NOT BACKING DOWN”

In a letter published by supporters at the weekend, Sentsov said he was determined to continue his hunger strike, which has seen him lose around eight kilograms and agree to what he called “supportive medical therapy” but not forced feeding.

“Let’s see what happens, but everyone understands that I am not backing down so they (doctors) are preparing ways to further preserve my health,” Sentsov wrote.

Doctors have expressed fears that his kidneys could pack up.

Asked last week about whether he might swap Sentsov for a Russian journalist being held by Kiev in a case Moscow says is political, Putin sounded skeptical.

“(Sentsov was detained) not for journalistic activities, but for preparing a terrorist attack, for planning an explosion that targeted specific people. These are completely different things,” said Putin.

Ukrainian authorities have called for a boycott of the World Cup and said the case of Sentsov and other prisoners are examples of Russian human rights abuses and militarism.

Some Ukrainian lawmakers even want to ban Ukrainian TV channels from broadcasting the tournament.

Amnesty International is also trying to use the World Cup to highlight what it says is the unjust fate of two rights defenders detained in Russia.

The Kremlin says it is up to the relevant courts to decide the men’s fate and that it does not intervene in such cases.