The United States has issued satellite images and cited intelligence to back its allegation Iran was behind attacks on major Saudi oil facilities.
One of the US government's satellite images showing apparent damage. Photo: US Government
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 percent and prices have soared.
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 a west-north-west direction - 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 Saudi-led coalition fighting in Yemen has accused Iran of providing the weapons.
A close-up image of damaged tanks at the Abqaiq processing plant (included above) appeared to show impact points on the western side.
Other images seem to show damage at the Khurais oilfield, which is located further west.
Apparent damage from the drone attacks. Photo: US Government
Iraq denied at the weekend that the attacks were launched from its territory. Prime Minister Adel Abdul Mahdi said Mr Pompeo had assured him in a phone call on Monday that the US backed Iraq's position.
Officials quoted by The New York Times said a mix of drones and cruise missiles might have been deployed, but that not all had hit their targets at Abqaiq and Khurais.
China and the European Union have, separately, urged restraint.
UN Yemen envoy Martin Griffiths told the Security Council on Monday it was "not entirely clear" who was behind the strike but he said it had increased the chances of a regional conflict.
In the UK, Foreign Secretary Dominic Raab also said it was not yet clear who was responsible, but called the act a "wanton violation of international law".
How the oil markets reacted
The oil price has seen the biggest one-day rise since the 1991 Gulf War, rising 20 percent but falling back later.
The international benchmark used by traders, Brent crude, jumped to $US71.95 a barrel at one point.
Prices eased after President Trump authorised a possible release of US reserves.
US Energy Secretary Rick Perry told business channel CNBC that it was too early to tell if this would be necessary. He also blamed Iran for the attack.
There are concerns that higher prices could continue if tensions worsen further.
Earlier Mr Perry insisted the oil market "is resilient and will respond positively".
- BBC
