Ukraine and the U.S. will use all opportunities to prevent further escalation, head of the Office of the President of Ukraine Andriy Yermak said.

"Zelensky just spoke to @POTUS. The most important thing right now is to prevent further escalation, and Ukraine and the U.S. will seize every opportunity to do so," he tweeted on Monday night.

"We are grateful to our American partners for supporting the Ukrainian sovereignty and territorial integrity of our state. The frequency of high-level contacts between Ukraine and the U.S. speaks of unprecedented support and complete mutual understanding," Yermak said.

Earlier it was reported that U.S. President Joseph Biden, in a telephone conversation with Ukrainian President Volodymyr Zelensky on Sunday evening, assured of the readiness of the U.S. and its allies to give a decisive response to possible aggression from Russia.