United States President Donald Trump said his country was "locked and loaded" to respond after drone attacks on two Saudi oil plants, which have threatened global oil supplies.
Washington has placed the blame with Iran for the attacks, which were claimed by Houthi rebels in Yemen.
“There is reason to believe that we know the culprit," Mr Trump tweeted on Sunday.
"We 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.”
The explosions, which took place on Saturday, set off fires that engulfed the Abqaiq plant, the world's largest oil processing facility, and nearby Khurais, which has a massive oilfield.
Earlier on Sunday, US Secretary of State Mike Pompeo accused Tehran of carrying out the strikes, saying there was “no evidence” the drones had come from Yemen.
China on Monday urged the US and Iran to "exercise restraint", with Foreign Ministry spokesperson Hua Chunying adding that it was not responsible to accuse others "in the absence of a conclusive investigation or verdict".
A US official said there were 19 points of impact in the attack on the Saudi plants, and that evidence showed the launch area was west-north-west of the targets, not south from Yemen.
Iran’s Foreign Minister, Javad Zarif, has denied Tehran’s involvement.
Iraq denied on Sunday that its territory had been used to carry out the attacks. Prime Minister Adel Abdul Mahdi received a phone call from Mr Pompeo on Monday, but his office did not specify what was discussed.
Saudi Aramco said the production of 5.7 million barrels of crude a day had been suspended after the attack but that work was under way to restore production.
Oil prices surged as the market opened Monday in Asia.
Brent crude jumped as much as US$11.73 to $71.95 a barrel, while West Texas Intermediate, another major benchmark, rose 15 per cent to $63.34.
A spokesman for the Houthi rebels, Yahia Sarie, said further strikes were to be expected, and that 10 drones had hit the Aramco facilities.
Mr Trump authorised the release of oil from the US's emergency oil reserves after the attacks knocked out half of the kingdom’s crude output.
In tweets, the president said the amount of oil released would be “sufficient to keep the markets well supplied”. He later said: “Plenty of oil.”
Russia's energy minister Alexander Novak said on Monday that he planned to have a phone call with his Saudi counterpart.
He said there was enough oil in commercial stockpiles worldwide to cover the shortfall of supplies from Saudi Arabia.
Mr Novak told reporters that the parameters of the global oil output deal had not been changed and there is no immediate need to convene an extraordinary Opec and non-Opec meeting.
Sheikh Mohamed bin Zayed expressed the UAE’s solidarity with the Kingdom in a phone call with Saudi Crown Prince Mohammed bin Salman on Sunday.
The Crown Prince of Abu Dhabi and Deputy Supreme Commander of the Armed Forces reaffirmed the country’s support for all of the measures taken by the kingdom to ensure the security and safety of its citizens, and all of those living on its soil.
“UAE and Saudi Arabia are standing as partners in facing besetting challenges. Our shared goals are the security of our nations," Sheikh Mohamed said in comments reported by Wam.
Mr Trump called the Saudi crown prince on Saturday to affirm his country's "readiness to co-operate with the kingdom by all means to maintain its security and stability", the Saudi Press Agency reported.
As tension continues to rise between Washington and Tehran, Mr Trump has left open the possibility of meeting his Iranian counterpart Hassan Rounani. But Iran on Monday ruled out any hope of that happening at the United Nations General Assembly in New York next week.
"Neither is such an event (a Trump-Rouhani meeting in New York) on our agenda, nor will it happen. Such a meeting will not take place," Foreign Ministry spokesperson Abbas Mousavi said in remarks carried by state TV. Tehran has repeatedly rejected such a meeting.
Mr Mousavi rejected as "nonsense" remarks by the Republican Senator Lindsey Graham that it was time for the United States "to put on the table an attack on Iranian oil refineries".