Drones launched by Yemen's Iranian-backed Houthi rebels hit key Saudi Arabian oil installations Saturday, setting off fires at a major oil processing facility and oilfield, according to Saudi and rebel officials.

The facilities are operated by Saudi Aramco, Saudi Arabia's state-owned oil giant, and produce up to 70% of the country's crude oil output.

Rising smoke from the fires at the sites could be seen by satellites in space.

President Donald Trump discussed the attacks with Saudi Crown Prince bin Salman in a phone call Saturday to "offer his support for Saudi Arabia's self-defense," according to White House deputy press secretary Judd Deere.

"The United States strongly condemns today’s attack on critical energy infrastructure," Deere said. "Violent actions against civilian areas and infrastructure vital to the global economy only deepen conflict and mistrust. The United States Government is monitoring the situation and remains committed to ensuring global oil markets are stable and well supplied.”

The official Saudi Press Agency, quoting an an interior ministry spokesperson, said the fires at the facilities in Abqaiq and Khurais were under control. The ministry confirmed that the blazes erupted after the facilities were hit by drones around 4 a.m.

The Wall Street Journal, quoting "people familiar with the matter," reported that Saudi Arabia is shutting down about half of its oil output following the strikes.

The shutdown would amount to a loss of about 5 million barrels a day, the Journal said, quoting its source, or roughly 5% of the world's daily production of crude oil.

The attack had no immediate impact on global oil prices as markets were closed for the weekend, the Associated Press reports. Benchmark Brent crude had been trading at just above $60 a barrel.

U.S. Ambassador to Saudi Arabia John Abizaid said on Twitter that Washington "strongly" condemned the attacks.

"These attacks against critical infrastructure endanger civilians, are unacceptable and sooner or later will result in innocent lives being lost," he wrote.

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In a short address aired by the Houthi’s Al-Masirah satellite news channel, military spokesman Yahia Sarie said the rebels launched 10 drones in their coordinated attack on the sites after receiving “intelligence” support from those inside the kingdom. He warned that attacks by the rebels would only get worse if the war continues.

“The only option for the Saudi government is to stop attacking us,” Sarie said.

Saturday's drone attack was only the latest against the Saudi oil infrastructure by Houthi rebels who are themselves in a war against a Saudi-led coalition aided by U.S. logistical and intelligence assistance.

Since the start of the war in 2015, Houthi rebels have been using drones in combat. The first appeared to be off-the-shelf, hobby-kit-style drones. Later, versions nearly identical to Iranian models turned up. Iran denies supplying the Houthis with weapons, although the U.N., the West and Gulf Arab nations say Tehran does.

In August, a Houthi-claimed attack sparked a fire at Aramco's Shaybah natural gas liquefaction facility but no casualties were reported by the company, Al Jazeera reports.

The rebels hold Yemen’s capital, Sanaa, and other territory in the Arab world’s poorest country. Since 2015, a Saudi-led coalition has fought to reinstate the internationally recognized Yemeni government.

The war has generated the world’s worst humanitarian crisis, pushing the country to the edge of famine and killed more than 90,000 people since 2015, according to the U.S.-based Armed Conflict Location & Event Data Project, which tracks the conflict.

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

The facility turns sour crude oil into sweet crude, then sends it to transshipment points on the Persian Gulf and the Red Sea or to refineries for local production. It can process and estimated 7 million barrels of crude oil a day, or around 70% of Saudi Arabia's recent daily output of more than 9 million barrels of crude oil a day.

The plant has been targeted in the past by militants. Al-Qaeda-claimed suicide bombers tried but failed to attack the oil complex in February 2006.

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.

Contributing: Associated Press