Saudi Arabia scrambled Sunday to restore operations at its key oil fields after drone attacks cut the kingdom's production in half, while also saying it would tap its vast reserves to shore up exports to the world market.

Meanwhile, there was widespread uncertainty about responsibility for the attacks that cut the Saudi oil production by 5.7 million barrels of oil a day - nearly 6% of the world's crude supply - and where the early Saturday missile attacks were launched.

Yemen's Iranian-backed Houthi militia claimed responsibility for the attacks, but U.S. Secretary of State Mike Pompeo blamed Iran and ruled out Houthi involvement.

"Tehran is behind nearly 100 attacks on Saudi Arabia while Rouhani and Zarif pretend to engage in diplomacy," Pompeo said on social media, referring to Iran's President Hassan Rouhani and Foreign Minister Mohammed Javad Zarif.

"Amid all the calls for de-escalation, Iran has now launched an unprecedented attack on the world's energy supply. There is no evidence the attacks came from Yemen," he said in a tweet. But he offered no evidence for his claim about Iran's involvement.

Tehran dismissed Pompeo's claim, with Zarif saying, "Having failed at 'max pressure,' U.S. Secretary of State Mike Pompeo turning to 'max deceit.'"

Some Iraqi media said the attack was launched from Iraq, which is closer to the Saudi oil production facilities than Yemen and where Iranian-backed paramilitary groups are entrenched. But the Iraqi government denied it was the launch site and vowed to punish anyone who uses its territory for attacks.

Saudi Arabia did not immediately lay blame for the attacks, but the kingdom's de facto ruler, Prince Mohammed bin Salman, said it was "willing and able" to respond to the "terrorist aggression." For decades, Sunni Muslim Saudi Arabia has been pitted against Shi'ite Iran in a struggle for regional domination and is locked in a nearly five-year conflict in Yemen, where a Saudi-led coalition has been battling the Houthis for dominance in the country in what is widely viewed as a proxy war between Saudi Arabia and Iran.

It was unclear how long it might take Riyadh to resume full operations at its state-owned Saudi Aramco production facilities. One source familiar with the destruction caused by the drone attacks told Reuters it could take "weeks, not days."

Saudi Arabia said it would compensate for the production loss by tapping in to its reserves of 188 million barrels of crude, with Saudi Aramco telling one Indian refinery there would be no immediate impact on deliveries. Oil analysts said the damage at the Saudi production sites could boost Friday's benchmark $55-a-barrel oil price by $3 to $5 a barrel on Monday.

The Saudi Embassy in Washington said U.S. President Donald Trump assured Prince Mohammed in a phone call that the U.S. was ready to help Riyadh to protect its security in the aftermath of the drone attacks.

White House adviser Kellyanne Conway told Fox News Sunday that the U.S. Energy Department could also tap its Strategic Petroleum Reserve to sell oil on the world market to stabilize the global energy supply.

Trump in recent days has said that he could meet with Iran's Rouhani at the United Nations General Assembly later this month as tensions mount over the U.S. leader's withdrawal last year from the 2015 international pact to restrain Iran's nuclear weapons and his reimposition of economic sanctions that have hobbled Iran's economy.

Conway said the attack on the Saudi oil fields "did not help" the prospects for Trump talks with Rouhani, but "he'll consider it. The conditions must be right for this president to take a meeting."

Amateur video of the middle-of-the night attack on the Saudi Aramco facilities in Abqaiq, in eastern Saudi Arabia, showed several blazes raging. By afternoon, video showed huge plumes of smoke rising into the sky. Saudi officials said no workers were killed or injured in the attacks.

A military spokesman for Yemen's Houthi militia, Col. Yahya Saree, said 10 Houthi drones hit the oil facilities, with the attacks being dubbed "Operation Balance of Terror." He said the attacks were a response to what he called the "ongoing crimes of blockade and aggression on Yemen" since the Saudi-led coalition began battling the Houthis five years ago.

Saree claimed the attack was the "largest to date" and that it "required extensive intelligence preparations," including information from sources inside Saudi Arabia.