Washington says that satellite images show the attack was not launched from Yemen as Houthi rebels claimed. Oil prices have surged in the wake of the attack.
The United States doubled down on its claim that Iran was behind attacks on Saudi oil refineries on Sunday, despite Houthi rebels saying they launched the attack from Yemen.
US President Donald Trump said "there is reason to believe that we know the culprit," adding that Washington is "locked and loaded" to respond, pending verification and information from Saudi Arabia.
Satellite images released by the US and examined by the Associated Press show around 17 "points of impact" at an oil processing facility in Abqaiq. Another two points of impact were found at Saudi's Khurais facility.
Senior US officials told reporters that damage indicates the attack was launched from the direction of Iraq and Iran and not from the south from Yemen.
One official, speaking on condition of anonymity, also said there were indications that cruise missiles were used, reported Reuters news agency.
Shortly following the Saturday attacks, Iran-backed Houthi rebels in Yemen claimed responsibility, saying they had carried out the strike with 10 unmanned drones.
A separate satellite image released by the European Commission appears to show black char marks at the heart of the oil processing facility in Abqaiq.
So far, neither Saudi Arabia nor state oil giant Saudi Aramco have said how much damage was done to the site, but global oil prices shot up after the country cut its oil production by more than half.
Oil prices surge
Oil prices shot up by more than 10% when markets reopened on Monday. US crude oil rose by $5.61 (€5.07) to hit $60.46 (€54.60) per barrel.
Brent crude oil surged to $7.84 to $68.06 per barrel, marking a 13% rise.
The strike forced Saudi Arabia to substantially curb its oil output, cutting back more than 5% of global oil supply. Analysts had expected oil prices to rise by $5 to $10 per barrel, but said that the long-term impact on the price will depend on how long production is disrupted.
On Sunday evening, Trump also said he approved the release of oil from US reserves following the attack.
"Based on the attack on Saudi Arabia, which may have an impact on oil prices, I have authorized the release of oil from the Strategic Petroleum Reserve, if needed, in a to-be-determined amount," Trump tweeted.
Iran dismisses 'maximum lies'
The attacks have inflamed tensions in the Persian Gulf, with both Iran and Iraq denying involvement.
"The Americans adopted the 'maximum pressure' policy against Iran, which, due to its failure, is leaning toward 'maximum lies,'" Iranian Foreign Ministry spokesman Abbas Mousavi said in a statement.
Earlier, US Secretary of State Mike Pompeo claimed there was no evidence that the attack originated from Yemen.
Iraqi Prime Minister Adel Abdul-Mahdi also denied reports that the drone attack was launched from its territory. His office released a statement saying that Iraq "abides by its constitution that prevents the use of its lands to launch aggressions against neighboring countries."
A Saudi-led coalition has been battling Iran-backed Houthi rebels in Yemen for over four years, with the Houthi's carrying out several cross-border missile and drone attacks.rs/aw (AP, Reuters)
