The US has essentially ruled out the possibility of assigning its armed forces to intercept Russian missiles and drones that are fired as part of the special military operation in Ukraine, even after Washington helped Israel repel an aerial attack from Iran.

"Different conflicts, different airspace, different threat picture," US National Security Council spokesman John Kirby said at a news conference, when asked whether this option was realistic.

He said he had anticipated the question, but US President Joe Biden had made it clear that the US would not take on a combat role in Ukraine.