In the United States and Europe, there is growing uncertainty about how to counter Putin’s aggression without stoking a direct conflict with Russia.

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.

A close ally of President Vladimir Putin warned Western governments on Thursday that a nuclear war would ensue if they gave the green light for Ukraine to use long-range Western weapons to strike targets deep inside Russia.