NEW YORK (AP) — Margaret Atwood, Stephen Sondheim and Patrick Stewart are among dozens of artists and journalists calling for the release of Ukrainian filmmaker and dissident Oleg Sentsov.

Sentsov, a critic of Russia's annexation of Crimea, is serving a 20-year term on terrorism charges. Sentsov, 41, has been on a hunger strike for three weeks, demanding the release of 64 Ukrainian political prisoners. He is not calling for his own release.

In a letter released Monday through PEN America, the artists called on Russian President Vladimir Putin to free Sentsov. They wrote that the upcoming World Cup games in Russia would heighten scrutiny of the country's human rights abuses. Freeing Sentsov would make a "powerful statement," they wrote.

Others signing the letter include Christiane Amanpour, John Green and Jonathan Franzen.