With two months left in office, lame-duck US President Biden made a major policy change that yields to a long-standing request from Ukraine as it fights the Russian invasion, now in its third year.

Biden administration officials say that they have minimal contact with their successors, noting that transition teams still have not signed the memorandums of understanding that would facilitate the briefings and conversations that are typically done ahead of a handoff.

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.