“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 on Sunday.

He said he had 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.

“Based on the attack on Saudi Arabia, which may have an impact on oil prices, I have authorised the release of oil from the Strategic Petroleum Reserve, if needed, in a to-be-determined amount sufficient to keep the markets well-supplied,” Trump said.

Oil prices surged more than 15 per cent at the open on Sunday on worries over global supply and soaring tensions in the Middle East. State oil giant Saudi Aramco said the attack on Saturday had cut output by 5.7 million barrels per day.

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.

Iranian Foreign Ministry spokesman Abbas Mousavi dismissed the US allegation it was responsible as “pointless”.

A senior Revolutionary Guards commander warned that the Islamic Republic was ready for “full-fledged” war.

“All American bases and their aircraft carriers in a distance of up to 2,000 kilometres around Iran are within the range of our missiles,” the semi-official Tasnim news agency quoted Commander Amirali Hajizadeh as saying.

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 that 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.

Saudi Arabia has not yet blamed any party for Saturday’s strike. Riyadh also says Tehran arms the Houthis, a charge both deny.

US Secretary of State Mike Pompeo said earlier that 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,” he said.

Some Iraqi media outlets said the attack came from there. Baghdad denied that on Sunday and vowed to punish anyone using Iraq, where Iran-backed paramilitary groups wield increasing power, as a launch pad for attacks.

Regional tensions have escalated since Washington quit an international nuclear deal and extended sanctions on Iran.

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.

But Trump appeared on Sunday to play down the chances he might be willing to meet with Iranian officials, saying reports he would do so without conditions were not accurate.

-AAP

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