The United States has issued satellite images and cited intelligence to back its claim that Iran was behind attacks on Saudi oil facilities.
Iran denies involvement in Saturday's air attacks, which were claimed by Iran-aligned Houthi rebels in Yemen.
But unnamed US officials speaking to US and international media say the direction and extent of the attacks cast doubt on Houthi involvement.
The incident has cut global oil supplies by 5% and prices have soared.
What is the US saying?
Secretary of State Mike Pompeo blamed Iran at the weekend, without providing any evidence, prompting Tehran to accuse Washington of deceit.
Tweeting on Sunday, President Donald Trump stopped short of directly accusing Iran, but suggested possible military action once the perpetrator was known.
Unnamed US officials have been speaking to the New York Times, ABC and Reuters.
One official said there were 19 points of impact on the targets and the attacks had come from the west and north-west – not Houthi-controlled territory in Yemen, which lies to the south-west of the Saudi oil facilities.
The officials said that could suggest launch sites in the northern Gulf, Iran or Iraq.
A close-up image of damaged tanks at the Abqaiq processing plant appeared to show impact points on the western side.
Officials quoted by the New York Times said a mix of drones and cruise missiles might have been deployed, but that not all hit their targets at Abqaiq and the Khurais oilfield.
ABC quotes a senior US official as saying that Mr Trump was fully aware that Iran was responsible.