Russia has sentenced an Australian man to 13 years in a maximum-security prison for fighting alongside Ukrainian forces, state prosecutors in the Russian-controlled parts of eastern Ukraine said Friday.

Russia and Ukraine agreed to exchange 1,000 prisoners of war each during peace talks held in Istanbul on Friday, in what would be the biggest prisoner swap of the conflict. The negotiations, which lasted less than two hours and were mediated by Turkey, marked the first time the nations have engaged in direct peace talks since the war began.

Oscar Jenkins, 33, will serve the sentence in a maximum security prison after being found guilty by a Russian court of participating in an armed conflict as a mercenary, state prosecutors in a part of eastern Ukraine controlled by Russia said on Friday.