The US has reportedly identified locations in Iran from which drones and cruise missiles were launched against major Saudi oil facilities on Saturday.
A senior US official told CBS News that the locations were in southern Iran, at the northern end of the Gulf.
Saudi air defences did not stop the drones and missiles because they were pointed southwards, to prevent attacks from Yemen, the official added.
Iran denies involvement in the attacks, which disrupted global oil supplies.
Yemen's Iran-aligned Houthi rebels said they had launched the drones that struck the Abqaiq oil processing plant, the world's largest, and the Khurais oilfield.
They have attacked Saudi oil facilities before but US officials said on Sunday they believed the drones and missiles did not originate from the south or south-west, and instead were launched from the north or north-west.
Iranian President Hassan Rouhani has called the attack a reciprocal act by the "Yemeni people".
Oil prices soared 20% after the attacks but have since pared their gains after reports from Saudi officials saying production levels could be back to normal within a matter of weeks – suggesting market disruption may not last as long as feared.
Brent crude – the international benchmark used by traders – was trading at about $66.10 (£52.89) on Tuesday, having reached $71.95 (£57.53) a barrel at one point in the wake of the attacks.
What has the US said?
President Donald Trump said on Monday it looked like the attacks had come from Iran, and US officials said they were gathering evidence to prove it.
A senior US official told CBS News that a US team had been on the ground at Abqaiq and identified specific drones and missiles used in the attacks.
This wreckage will be analysed and used to present "a very compelling forensic case" that Iran was responsible, the report says.
Vice-President Mike Pence said on Tuesday the US was "evaluating all the evidence", and that Secretary of State Mike Pompeo was en route to Saudi Arabia "to discuss our response".
He added: "The United States of America will take whatever action is necessary to defend our country, our troops, and our allies in the Gulf. You can count on it."
Iranian Foreign Minister Javad Zarif tweeted that "Yemeni victims" were responsible for the attacks, saying that blaming Iran would not change the situation and saying the US was "in denial".
Ending the war was the "only solution for all," he added.
And in a televised address, Iran's Supreme Leader Ayatollah Ali Khamenei dismissed talks "at any level" with the US, saying any dialogue could only happen if the US "takes back its words and repents" after withdrawing from the Iran nuclear deal.
Earlier this year, President Trump unilaterally pulled the US out of the landmark agreement that had limited Iran's nuclear programme in exchange for the lifting of economic sanctions.
This is the strongest claim yet from the Americans that the attacks against the Saudi oil facilities were launched from Iran itself.
No corroborating evidence or intelligence has yet been provided. But if true, it takes the Gulf crisis to a more dangerous level and it demonstrates a new threshold of brinkmanship by the Iranian authorities. It also raises the question: what response, if any, is required?
For past US presidents the security of oil supplies in the Gulf was an absolute priority. But for the "locked and loaded" Donald Trump, for all his bluster and apparent affinity with the Saudi royal family, thRead More – Source