President Donald Trump warned Tuesday that the United States may strike Iran again, a day after he said he had held off a major assault in hope of a deal to end the war -- but Tehran's army threatened to open "new fronts" if he went ahead.

Trump told reporters at the White House that he had been just "an hour away" from relaunching Washington's attacks on Iran before postponing the order, after weeks of a fragile ceasefire and talks to end the war that began on February 28.

"You know how it is to negotiate with a country where you're beating them badly. They come to the table, they're begging to make a deal," he said.

"I hope we don't have to do the war, but we may have to give them another big hit. I'm not sure yet."

But Iran's army spokesman Mohammad Akraminia earlier warned the Islamic republic would "open new fronts against" the United States if it restarted its attacks.