Biden has committed tens of billions of dollars to Kyiv's war effort, and at the weekend he reportedly ditched a long-standing red line on Ukraine's use of American weaponry to launch attacks deep into Russia. Donald Trump Jr tweeted that the president was trying to "get World War Three going" before his father took office.

President Joe Biden for the first time authorized Ukraine to use U.S.-given long-range missiles to strike inside Russia, a prospect that Trump allies believe could threaten "World War III."

President Joe Biden's apparent green light for Ukraine to strike Russia with US-made long-range missiles has caused consternation among Donald Trump's allies. Trump himself has not commented, but he won the election after promising to end the war - and people close to him have condemned the move as dangerous escalation.

The Kremlin said on Monday that Russia would respond to what it called a reckless decision by Joe Biden's administration to allow Ukraine to fire American missiles deep into Russia, which it said would draw the United States directly into the conflict.