The conflict between Ukrainian troops and Russian-backed forces in eastern Ukraine arose. Heavy fighting erupted in eastern Ukraine, the country's military said, while separatists blamed Ukraine.
Ukrainian President Volodymyr Zelenskiy said he would convene a national security council meeting to discuss the latest flare-up in the country's Donbass region.
“This is not just a cynical provocation… it is an attempt to disrupt the peace process in the Donbass, which had begun to move through small but continuous steps,” Zelenskiy said in a statement.
The separatists who receive Russian support accused Ukrainian government forces of attacking first, saying a small group of soldiers had tried and failed to break through their lines.
The Kremlin said it had seen reports of the clashes and was looking into them. It said it did not know what had triggered the violence.
Ukraine, Western countries and NATO accuse Russia of sending troops and heavy weapons to prop up separatist fighters in Donbass, a charge that Moscow has denied.
Zelenskiy came to power last year promising to end the conflict. Since then, Ukraine and Russia have implemented some confidence-building measures, including prisoner swaps and phased troop withdrawals in designated areas.
Zelenskiy and Russian President Vladimir Putin spoke by phone last week, the Ukrainian leader's office said.