Russia on Sunday invited United Nations and Red Cross experts to probe the deaths of dozens of Ukrainian prisoners held by Moscow-backed separatists, while Ukraine's president ordered the evacuation of residents in the eastern region of Donetsk.
President Volodymyr Zelenskiy said hundreds of thousands of people were still exposed to fierce fighting in the Donbas region, which contains Donetsk and Luhansk province.
Ukraine and Russia have traded accusations over a missile strike or explosion early on Friday that appeared to have killed dozens of Ukrainian prisoners of war in the front-line town of Olenivka in eastern Donetsk.
Russia invited experts from the U.N. and Red Cross to probe the deaths "in the interests of conducting an objective investigation", the defense ministry said on Sunday.
Ukraine's armed forces denied responsibility, saying Russian artillery had targeted the prison to hide mistreatment there.