Trump also authorised the use of the US emergency oil stockpile to ensure stable supplies after the attack, which shut 5 per cent of world production and sent crude prices soaring more than 19 per cent in early trade on Monday, before moderating to show a 10 per cent gain.

There is reason to believe that we know the culprit, are locked and loaded depending on verification, but are waiting to hear from the Kingdom as to who they believe was the cause of this attack, and under what terms we would proceed!" Trump said on Twitter.

Earlier in the day, a senior US official told reporters that evidence from the attack, which hit the world's biggest oil-processing facility, indicated Iran was behind it, instead of the Yemeni Houthi group that had claimed responsibility.

US Secretary of State Mike Pompeo also said there was no evidence the attack came from Yemen, where a Saudi-led coalition has been battling the Houthis for over four years in a conflict widely seen as a proxy war between Saudi Arabia and Shi'ite Muslim rival Iran.

"Amid all the calls for de-escalation, Iran has now launched an unprecedented attack on the world's energy supply," Pompeo said.

Iranian Foreign Ministry spokesman Abbas Mousavi dismissed the US allegations that it was responsible was "pointless". A senior Revolutionary Guards commander warned the Islamic Republic was ready for "full-fledged" war.

"All American bases and their aircraft carriers in a distance of up to 2000 kilometres around Iran are within the range of our missiles," the semi-official Tasnim news agency quoted Commander Amirali Hajizadeh as saying.

Tensions between Washington and Tehran were already running high because of a long-running dispute between the two nations over Iran's nuclear program that led the US to impose sweeping sanctions.

The US official, who asked not to be named, said on Sunday there were 19 points of impact in the attack on Saudi facilities and evidence showed the launch area was west-northwest of the targets - not south from Yemen.

The official added that Saudi officials indicated they had seen signs that cruise missiles were used in the attack, which is inconsistent with the Iran-aligned Houthi group's claim that it conducted the attack with 10 drones.

"There's no doubt that Iran is responsible for this. No matter how you slice it, there's no escaping it. There's no other candidate," the official told reporters.

Riyadh has accused Iran of being behind previous attacks on oil-pumping stations and the Shaybah oil field, charges that Tehran denies, but has not blamed anyone for Saturday's strike. Riyadh also says Tehran arms the Houthis, a charge both deny.

Riyadh said it would compensate for the damage at its facilities by drawing on its stocks, which stood at 188 million barrels in June, according to official data.

UN Secretary-General Antonio Guterres condemned Saturday's attacks and called on all parties to exercise restraint and prevent any escalation.

The attack came after Trump said a meeting with Iranian President Hassan Rouhani was possible at the UN General Assembly in New York this month. Tehran ruled out talks until sanctions are lifted.

Australian Associated Press