Dubai, United Arab Emirates — Iran denied it was involved in drone attacks that hit the world's biggest oil processing facility and an oil field in Saudi Arabia. The denial came just hours after America's top diplomat alleged that Tehran was behind the "unprecedented attack on the world's energy supply."

Yemen's Houthi rebels had claimed responsibility for the attacks, which led to the interruption of an estimated 5.7 million barrels in oil supplies. Saudi Arabia pledged stockpiles would make up the difference.

This Saturday, Sept. 14, 2019, satellite image from Planet Labs Inc. shows thick black smoke rising from Saudi Aramco's Abqaiq oil processing facility in Buqyaq, Saudi Arabia. Planet Labs Inc via AP

Iranian Foreign Ministry spokesman Abbas Mousavi on Sunday dismissed Pompeo's remarks as "blind and futile comments."

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"The Americans adopted the 'maximum pressure' policy against Iran, which, due to its failure, is leaning towards 'maximum lies'," Mousavi said in a statement.

While markets remained closed Sunday, the attack could shock world energy prices. They also increased overall tensions in the region.

Late Saturday, U.S. Secretary of State Mike Pompeo directly blamed Iran for the attack on Twitter, without offering evidence to support his claim.

"Amid all the calls for de-escalation, Iran has now launched an unprecedented attack on the world's energy supply," Pompeo wrote. "There is no evidence the attacks came from Yemen."

CBS News senior foreign affairs correspondent Margaret Brennan reports that the reason Pompeo said there is no evidence the attack came from Yemen is because 15 structures at Abqaiq in Saudi Arabia reportedly suffered damage on their west-northwest facing sides. The Houthis media site claims 10 drones targeted the oil refineries in eastern Saudi Arabia. But the U.S. thinks it would be tough for Houthis to have hit west or northwest Saudi from the south.

"We call on all nations to publicly and unequivocally condemn Iran's attacks," Pompeo tweeted.

The U.S., Western nations, their Gulf Arab allies and U.N. experts say Iran supplies the Houthis with weapons and drones - a charge that Tehran denies.

U.S. officials previously alleged at least one recent drone attack on Saudi Arabia came from Iraq, where Iran backs Shiite militias. Those militias in recent weeks have been targeted themselves by mysterious airstrikes, with at least one believed to have been carried out by Israel.

Separately, Iraqi Prime Minister Adel Abdul-Mahdi's office issued a statement on Sunday denying the drone attack came from there.

Iraq "abides by its constitutions that prevents the use of its lands to launch aggressions against neighboring countries," the statement said.

First word of Saturday's assault came in online videos of giant fires at the Abqaiq facility, some 205 miles northeast of the Saudi capital, Riyadh.

Machine-gun fire could be heard in several clips alongside the day's first Muslim call to prayers, suggesting security forces tried to bring down the drones just before dawn. In daylight, Saudi state television aired a segment with its local correspondent near a police checkpoint, a thick plume of smoke visible behind him.

President Donald Trump called Saudi Arabia's Crown Prince Mohammed bin Salman to offer his support for the kingdom's defense, the White House said. The crown prince assured Mr. Trump that Saudi Arabia is "willing and able to confront and deal with this terrorist aggression," according to a news release from the Saudi Embassy in Washington.

Saudi Aramco describes its Abqaiq oil processing facility in Buqyaq as "the largest crude oil stabilization plant in the world."

The facility processes sour crude oil into sweet crude, then transports it onto transshipment points on the Persian Gulf and the Red Sea or to refineries for local production. Estimates suggest it can process up to 7 million barrels of crude oil a day. By comparison, Saudi Arabia produced 9.65 million barrels of crude oil a day in July.

The Khurais oil field is believed to produce over 1 million barrels of crude oil a day. It has estimated reserves of over 20 billion barrels of oil, according to Aramco.

There was no immediate impact on global oil prices as markets were closed for the weekend. Benchmark Brent crude had been trading at just above $60 a barrel.