US President Donald Trump has cut short his visit to the Group of Seven summit in Canada, with the White House saying he must return to Washington to deal with the escalating conflict between Iran and Israel.

"I have to be back early for obvious reasons," Trump said, as reports circulated he had instructed the White House National Security Council to meet upon his return.

US Defence Secretary Pete Hegseth earlier announced the "deployment of additional capabilities" to the Middle East to enhance the Pentagon's "defensive posture" in the region.

But American officials rejected suggestions that the US was about to join Israeli offensive operations against Iran.

The White House was at pains to emphasise that Trump had "a great day" at the summit, saying much was accomplished, including a trade deal between the US and UK.