STORY: Dozens of Ukrainian prisoners of war appear to have been killed in a missile strike that destroyed a prison building on the frontline of the conflict.
This report contains graphic content of the incident.
The Russian and Ukrainian governments are accusing each other of carrying out the attack, which happened in the town of Olenivka. It's part of the Donetsk region held by separatists.
Reuters journalists saw charred human remains at the scene and shell fragments laid out on a bench, although it wasn't immediately possible to find any identifying markings on the fragments.
Nor was it clear where the fragments were collected.
Russia's defense ministry said 40 prisoners were killed and 75 wounded when the facility was targeted by rockets made in the United States. That's according to Russian news agencies.
A spokesman for Moscow-backed separatists said Ukrainian forces attacked after the prisoners of war started talking about crimes conducted by their own military.
"After the Ukrainian captives started sharing the information on the crimes they committed following the orders of their commanders, and that those commanders received the orders from Kyiv, the political leadership of Ukraine decided to use U.S.-produced multiple-launch rocket systems HIMARS to carry out a strike here to veil the crimes that the Ukrainian captives started talking about."
Ukraine's military denies carrying out the strike. It says it was Russian artillery that hit the facility, to hide the mistreatment of prisoners there, and then to blame Ukraine. Ukraine's foreign minister is calling it a war crime.
There was no way for Reuters to immediately verify either version of events.
Ukraine's government has accused Russia of atrocities against civilians throughout the conflict and says it has identified more than 10,000 possible war crimes.
Moscow denies involvement in war crimes and accuses Ukraine of staging them.