American officials have shared intelligence with Riyadh indicating that Iran was the staging ground for devastating drone attacks on Saudi Arabia's oil installations, the Wall Street Journal reported on Monday.
The weekend strikes on Abqaiq -- the world's largest processing plant -- and the Khurais oilfield have knocked out 5.7 million barrels per day (bpd), or six percent of global production, sending prices soaring.
While Washington has blamed Tehran, the Monday assessment on the origin of the attacks has not been shared publicly, the Journal said.
The US assessment determined that "Iran launched more than 20 drones and at least a dozen missiles," according to unnamed sources.
"But Saudi officials said the US didn't provide enough to conclude that the attack was launched from Iran, indicating the US information wasn't definitive," the WSJ added.
"US officials said they planned to share more information with the Saudis in the coming days."
President Donald Trump has said that the United States is ready to help Saudi Arabia, but will wait for a "definitive" determination on who was responsible.
"I'm not looking to get into new conflict, but sometimes you have to," he said. "That was a very large attack, and it could be met by an attack many, many times larger."
"Certainly, it would look to most like it was Iran."
Iran-supported Huthi rebels -- who are fighting a Saudi-led coalition in Yemen -- claimed the strikes.
Riyadh has said Iranian weapons were used, but stopped short of blaming Tehran directly.
Tensions between Iran and the US and its allies have threatened to boil over since May last year when President Donald Trump abandoned a 2015 nuclear deal and began reimposing sanctions in a campaign of "maximum pressure".
Iran responded by scaling back its commitments under the landmark accord, which had promised it sanctions relief in return for limiting the scope of its nuclear program.
Iran's supreme leader Ayatollah Ali Khamenei on Tuesday ruled out talks "at any level" with the United States.
The weekend attacks in Saudi Arabia have spiked tensions and prompted concerns about an escalation. Conflict in the Gulf region could put a large portion of global energy supplies at risk.
