Ukraine said on Thursday that Russia had handed over the bodies of 1,000 Ukrainian soldiers killed in the war between the two countries.

Ukraine’s Coordination Headquarters for the Treatment of Prisoners of War said in a statement that efforts were under way to identify the remains that were transferred.

“An exchange took place today, involving the return to Ukraine of 1,000 bodies that Russia said belonged to Ukrainian defenders,” the statement said, thanking the International Committee of the Red Cross for its support during the process.

Russian President Vladimir Putin’s adviser Vladimir Medinsky said in a post on social media that 1,000 bodies of Ukrainian soldiers were handed over to Ukraine under the Istanbul agreements, while Russia received the remains of 38 Russian soldiers.