Yemen's Houthi rebels took responsibility for the attacks, and Iran denied the USA allegations.
It was the worst such attack on regional oil facilities since Saddam Hussein torched Kuwait's oil wells during the 1990-91 Gulf war.
Trump restrained talk of quick military action, although earlier he had said the United States was "locked and loaded".
Indeed, Iran has now said Rouhani will not meet with Trump at the event. "These attacks resulted in production suspension of 5.7 million barrels of crude oil per day", Saudi Aramco said in a statement.
"Yemen is the target of daily bombings". The Guard shot down the USA drone on June 20.
"But Saudi officials said the U.S. didn't provide enough to conclude that the attack was launched from Iran, indicating the United States information wasn't definitive", the WSJ added.
Riyadh said its initial investigations indicate that Iranian weapons were used in the attacks on its key oil plants in Abqaiq and said it would "invite United Nations and worldwide experts to view the situation on the ground and to participate in the investigations".
That indicated they were fired from the northern Persian Gulf, Iran or neighbouring Iraq, where Iran backs various armed groups.
Washington called the assault, which sparked huge fires in the heart of Saudi Arabia's oil industry, an "unprecedented attack on the world's energy supply".
With the Huthis threatening further attacks, world powers urged restraint.
North Atlantic Treaty Organisation chief Jens Stoltenberg told AFP in Baghdad on Monday that he was "extremely concerned" about escalating tensions following the attacks, and accused Iran of "destabilising" the region.
Sensing a commercial opening, President Vladimir Putin said Russia was ready to help Saudi Arabia by providing Russian-made air defence systems to protect Saudi infrastructure. The kingdom, though, has not yet said where the attack was launched from or what kind of weapons were involved.
The Huthis said 10 drones struck the sites, but Saudi Arabia pointed the finger of blame at Iran. The sharp rise in oil prices that followed the attack dampened any chances of a positive reaction to government's economic stimulus package last week. The global benchmark used by traders, Brent crude, is now trading at around $65.34 (£52.32).
Frankly, White House rhetoric notwithstanding, Saudi Arabia's next steps will largely determine when and where outright war breaks out.
While Aramco is still assessing the state of the Abqaiq plant and the scope of repairs, it now believes less than half of the plant's capacity can be restored quickly, said people familiar with the matter, who asked not to be identified because the information isn't public.
"They're in the process of assessing the damage".
The Chinese state refiner was also told that some of its September-loading light crude cargoes will be swapped to heavier grades with no delays or change in volumes, the source said.
The fallout in Asia, the largest buyer of Saudi crude, has been varied, with some refineries expected to receive their allocated volumes for October, and other importers being told of delays or being offered alternative grades.
While the world was still grappling with the after-effects, one expert said there was one thing that he found most shocking about the drone-powered strike, which effectively wiped out half of the country's output.
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