Saudi Arabia's defence ministry has shown off what it says is the wreckage of drones and cruise missiles that proves Iranian involvement in weekend attacks on two oil facilities.
It said 18 drones and seven cruise missiles were fired from a direction that ruled out Yemen as a source.
Yemen's Iran-aligned Houthi rebels have said they are behind the attacks.
Iran has denied any involvement and warned it would retaliate against any attack that targeted it.
The US has stood by its accusation that Iran was behind the attacks. Secretary of State Mike Pompeo said after arriving in Saudi Arabia on Wednesday that it was an "act of war".
President Donald Trump said the US had "many options" in response.
"There is the ultimate option, and there are options a lot less than that," he said. "And we'll see. We are in a very powerful position."
Will Iran or for that matter the United States retaliate after deadly oil attacks?
Only time will tell, but the region, although being on heightened alert for many months, is now more volatile than it has been for many years.