KYIV, Oct. 22 - Pro-Russian separatists in eastern Ukraine said on Tuesday they had sentenced a journalist to 15 years in prison after a court found him guilty of spying on behalf of Ukraine’s SBU intelligence service, Reuters reported.

Stanislav Aseyev, 30, disappeared in Ukraine’s Donetsk region in June 2017 where he was working under a pen name for the Ukrainian service of U.S.-government-funded Radio Free Europe/Radio Liberty (RFE/RL), among other outlets.

A statement issued by the Prosecutor General’s office in the self-proclaimed People’s Republic of Donetsk said on Tuesday Aseyev had gathered military intelligence about the separatists and produced material showing them in a negative light.

It also accused him of recruiting others to gather intelligence on Ukraine’s behalf.

A court in August found him guilty of a raft of charges, including extremism and espionage, and sentenced him to 15 years in a penal colony, Tuesday’s statement said.

RFE/RL President Jamie Fly condemned Aseyev’s conviction.

“Stas (Stanislav) is a journalist and was only trying to raise awareness about the situation in eastern Ukraine. The ruling is an attempt by Russian-backed separatists in Donetsk to silence his powerful, independent voice. Stas should be released immediately.”

Ukraine’s Foreign Ministry condemned what it said was Aseyev’s illegal detention and “pseudo-conviction” and called on Russia to bring about his urgent release.

The U.S. Embassy in Ukraine said it was deeply concerned.

“We call on Russia and the forces it backs to immediately release him and other Ukrainians who have been unjustly detained,” it said in a statement on social media.

Kiev’s forces have been battling pro-Russian separatists in the Donbass region of eastern Ukraine since 2014, a conflict that has claimed more than 13,000 lives. Sporadic fighting continues despite a ceasefire agreement. (rt/ez)