US President Donald Trump said Wednesday the US-Israeli war campaign against Iran was almost complete but that the country would be hit hard over the next two to three weeks as Washington pressed toward its military objectives.

Speaking in his first national address since the war began on 28 February, Trump sought to reassure war-weary Americans that the offensive was worth the effort.

"Thanks to the progress we've made, I can say tonight that we are on track to complete all of America's military objectives shortly, very shortly," Trump said from the White House.

The war's "core strategic objectives are nearing completion," he said, cautioning however that "we are going to hit them, extremely hard, over the next two to three weeks."