Ukrainian President Petro Poroshenko said Russia was to blame for the latest flare-up in hostilities near the industrial town of Avdiyivka in eastern Ukraine which have led to the heaviest casualties for months.
"The full responsibility for the current sharp escalation of the situation around the Avdiyivka industrial zone ... lies with Russia and the fighters that it supports," he said in a statement.
Russian Foreign Minister Sergey Lavrov told his French counterpart Jean-Marc Ayrault that a flare-up of violence in eastern Ukraine may nullify two-year long efforts to pacify warring sides, Russia's foreign ministry said.
Mr Ayrault also told Mr Lavrov that Moscow should do everything to ensure the escalation ends in eastern Ukraine, where two years of negotiation have failed to bring peace.
They also discussed Syria in a phone call, it said.