U.S. missiles struck targets across Iran on Friday and President Donald Trump vowed "major military punishment" for Tehran and its Houthi allies in Yemen, though he once again left open the door to a diplomatic deal with Iran.

Two weeks after the collapse of an interim truce meant to end the ​war, the Iranian armed forces responded by firing at U.S. bases in neighbouring Arab countries and warning people there that they could strike non-military buildings used by U.S. personnel.

Trump has threatened in recent days to expand ‌the targets being struck in Iran to include energy plants and bridges, to send ground forces to seize its Kharg Island oil hub, and to bomb a deep-underground nuclear-linked site known as Pickaxe Mountain.

On Friday, he said he had not yet made a decision for new major strikes.

"We are talking to them. I think they're being serious. I think ... they are being by far the most serious that we've seen them, but that doesn't mean we get there," Trump told reporters at the White House.

Asked what is the exit strategy for the Iran war, Trump said: "There's a military exit where we just keep ​going just the way we are, and we can even make it a heavier dose, and it's knocking out everything they have. Or there's a smarter strategy that you make a deal."

But he added: "We're locked and loaded. We're ready to ​go."

The Strait of Hormuz, entrance to the Gulf, has so far been the focus of a war that has killed thousands in almost five months, stoked global inflation and fanned fears of ⁠an economic downturn.

The Houthis, who control northern and western Yemen, have also announced a naval blockade on Saudi Arabia, which has diverted millions of barrels of oil each day by pipeline to the Red Sea to skirt Iran's near-total blockade of Hormuz.

After the Houthis ​said they had struck two Saudi tankers in the Red Sea on Thursday, Trump said he would hold Iran accountable for any further attacks by the fighters.

The Saudi-led coalition in Yemen said it carried out strikes on Houthi military sites in Yemen's Hodeidah governorate ​on Friday, saying the sites were used to threaten commercial shipping.

The Houthi-affiliated Al Masirah TV said Saudi strikes hit facilities belonging to the state telecommunications corporation in Hodeidah city. The broadcaster also said Saudi forces targeted Kamaran Island, off Yemen's western coast.

-Reuters