Experts also said it was unlikely to have been the militia.
“This wasn’t done by an amateur, to put it very mildly,” tweeted Carl Bildt, co-chairman of the European Council on Foreign Relations.
At a press conference on Monday night, Donald Trump, the US president, said “it certainly would look” like Iran was behind the attack but added “we’ll let you know” as “that’s being checked out right now”.
"I'm not looking to get into a new conflict but sometimes you have to," he added.
Asked if a "lethal" US military strike would be a proportional response against those responsible, Mr Trump replied: "I would say yes."
"I'll have a stronger message, or maybe no message, depending on the results. There's no rush," he said.
"Personally, I'm not concerned at all, we have military power the likes of which the world has never seen."
Severe damage to the Abqaiq plant has halted production of 5.7 million barrels of crude a day briefly causing the biggest jump in oil prices since the 1991 Gulf War.
On Sunday, Mr Trump had tried in vain to reassure Americans there would not be a knock-on effect. “PLENTY OF OIL!”, he tweeted, followed by, “We don’t need Middle Eastern Oil & Gas, & in fact have very few tankers there, but will help our Allies!”.
Mr Trump has said he does not want war with Iran, despite pursuing a “maximum pressure” policy towards the nation which is refusing to sign a new treaty that would place indefinite curbs on its nuclear programme.
Britain condemned the attack on the oil facilities as “a wanton violation of international law” but said it was necessary to determine the facts before pursuing a response.
Dominic Raab, the Foreign Secretary, said: “In terms of who is responsible, the picture is not entirely clear.”
Hassan Rouhani, the Iranian president, clearly placed the blame on the Yemeni rebels. “The people of Yemen have been forced to respond, they are only defending themselves,” he told the Turkish media.
Saudi Arabia and the United States claimed they had evidence Iran was behind the weekend attack on the kingdom’s oil facilities on Monday.
Col Turki al-Malki, Saudi’s military spokesman, said Iranian weapons were used in Saturday’s strikes on the Khurais oilfield and the Abqaiq refinery, the world’s largest petroleum processing plant.
However, he did not openly blame Iran for the attack – which has knocked out five per cent of global crude oil production – suggesting the Saudis are trying to calm the increasingly tense situation before it spills into war.
Instead he said Riyadh would investigate where the drones were launched as he did not believe the Iran-backed Houthi militia who are fighting the Saudi-backed government in Yemen, was responsible for the attack as they had claimed.
“This strike didn’t come from Yemen as the Houthi militia are pretending,” Col al-Malki said. “It was a massive and highly sophisticated attack.”