"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 pricessurged 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 the Islamic Republic was ready for"full-fledged"war.