The Russian president issued his sternest warning to date about the use of Western weapons in Ukraine ahead of a meeting of British and U.S. leaders.

Russian President Vladimir Putin has warned NATO alliance leaders that a move to lift restrictions on Ukraine’s use of longer-range Western missiles to strike deep inside his country would be considered an act of war.

A senior Russian lawmaker on Thursday said that Ukrainian strikes on Russia with Western missiles would lead to global war with the use of nuclear weapons and that Moscow's response would be tough with more powerful weapons.