Saudi Arabia says drone attacks at two massive oil processing facilities have knocked out half of the country's total oil production.

Key points: The attacks have slashed the refineries' total production

The attacks have slashed the refineries' total production Iranian-backed Houthi rebels claimed responsibility for the attack

Iranian-backed Houthi rebels claimed responsibility for the attack Online videos showed huge flames engulfing the Abqaiq facility, with both blazes now under control

US Secretary of State Mike Pompeo blamed Iran for the attacks on the Saudi Aramco oil facilities, calling it an "unprecedented attack on the world's energy supply".

The drone raids on Saturday morning "resulted in a temporary suspension of production at Abqaiq and Khurais plants" Saudi energy minister Prince Abdulaziz bin Salman said in a statement carried by the official Saudi Press Agency.

He said the raids led to the interruption of an estimated 5.7 million barrels of crude, or about half of the country's total production.

Mr Pompeo said Iran was behind the attacks. ( Reuters )

There was no immediate impact on global oil prices as markets were closed for the weekend.

The International Energy Agency said it was monitoring the situation and that "for now, markets are well supplied with ample commercial stocks".

But Centre on Global Energy Policy director Jason Bordoff said the attack would see a "jump" in oil prices.

"Abqaiq is perhaps the most critical facility in the world for oil supply," he said. "The risk of tit-for-tat regional escalation that pushes oil prices even higher has just gone up significantly."

Iranian-backed Houthi rebels had earlier claimed responsibility for the raid on Abqaiq and a second drone strike on Khurais, the country's second largest oil field.

The Houthis are engaged in a war with Saudi-led forces in neighbouring Yemen.

A Houthi military spokesman said the attacks were carried out by 10 drones.

"These attacks are our right, and we warn the Saudis that our targets will keep expanding," spokesman Yahya Saree said in a statement read out on the rebels' Al Masirah TV.

"We have the right to strike back in retaliation to the air strikes and the targeting of our civilians for the last five years."

In a series of tweets, Mr Pompeo said "there is no evidence the attacks came from Yemen" and pointed the finger at Tehran.

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He added: "Iran has now launched an unprecedented attack on the world's energy supply."

The US and Iran have become increasingly combative since US President Donald Trump pulled out of an international agreement which curbed the Islamic Republic's nuclear program in return for an easing of economic sanctions on Iran.

Iran retaliated by resuming uranium enrichment, seen in the West as a potential conduit to it developing a nuclear bomb.

But it faces severe economic damage under intensified US sanctions designed to strangle its vital oil trade.

Trump pledges Saudi support

Mr Trump condemned the drone attacks following a phone call with Saudi Crown Prince Mohammed bin Salman.

"Violent actions against civilian areas and infrastructure vital to the global economy only deepen conflict and mistrust," the White House said in a statement.

Mr Trump offered the Crown Prince "his support for Saudi Arabia's self-defence," the White House said.

US Energy Secretary Rick Perry said the US was prepared to deploy resources from its Strategic Petroleum Oil Reserves if necessary, to "offset any disruptions to oil markets".

The US oil reserves holds 630 million barrels.

Houthi rebels ramp up firepower

Houthi rebels have a history of using drones to hit targets inside Saudi Arabia.

The first appeared to be off-the-shelf, hobby-kit-style drones but later versions appeared nearly identical to Iranian models.

The Houthis launched drone attacks targeting Saudi Arabia's crucial East-West Pipeline in May as tensions between Iran and the US grew.

Iran denies supplying the Houthis with weapons, although the UN, the West and Gulf Arab nations say Tehran is backing the rebel group.

UN investigators say the Houthis' new UAV-X drone probably has a range of up to 1,500 kilometres, putting the far reaches of both Saudi Arabia and the United Arab Emirates in range.

The blaze halted a day's production at the Abqaiq refinery. ( AP )

Videos posted online showed on Saturday showed giant flames leaping into the air at the Abqaiq facility, 330 kilometres north-east of the Saudi capital Riyadh.

Gunfire 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.

No workers were injured and the blazes "were controlled", the Saudi Energy Minister told the state-run press agency.

A Reuters witness said at least 15 ambulances were seen in the area and there was a heavy security presence around Abqaiq.

A NASA satellite image from Saturday shows smoke billowing across north-east Saudi Arabia. ( AP: NASA Worldview )

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