Drones launched by Yemen’s Houthi rebels hit two oil production facilities in Saudi Arabia Saturday, sparking huge fires that threatened global energy supply.

The Interior Ministry confirmed attacks in a statement carried by state-run Saudi Press Agency. The Iranian-backed Houthis claimed credit, saying 10 drones were used in the assault.

The attack sites are home to one of the world’s largest oil processing facilities and a major oil field, likely disrupting the kingdom’s oil production. The attacks are also likely to exacerbate tensions in the Persian Gulf amid the confrontation between the U.S. and Iran over a crippled nuclear deal.

U.S. President Donald Trump spoke with Saudi Crown Prince Mohammed bin Salman after the attacks, the White House said, adding it was committed to keeping oil markets well supplied.

“The United States strongly condemns today’s attack on critical energy infrastructure,” White House spokesman Judd Deere said. “Violent actions against civilian areas and infrastructure vital to the global economy only deepen conflict and mistrust.”

Secretary of State Michael Pompo blamed Iran for the attacks, saying there is no evidence that the attacks came from Yemen. Iran launched an “unprecedented attack on the world’s energy supply,” Pompeo said on Twitter

The coordinated strikes targeted two facilities in Saudi Arabia’s Eastern Province. The fires have already been put out, the Interior Ministry said.

The Wall Street Journal cited sources saying Saudi Arabia, the world’s top oil exporter, shut down about half its oil output after the attacks, resulting in a reduction of 5 million barrels a day, or roughly 5% of the world’s daily production.

Saturday’s attacks represent some of the largest launched by the Houthis, who have been targeting Saudi Arabia’s gas facilities, pipelines and tankers. A Saudi-led coalition of Sunni Muslim countries has been fighting the Houthis in Yemen since 2015 in what is widely seen as a proxy war with Shiite rival Iran.

The coalition launched airstrikes against a Houthi camp in Yemen on Saturday, according to Reuters.

Trump has hinted at the possibility of meeting with Iranian President Hassan Rouhani on the sidelines of the U.N. General Assembly meeting later this month. But the latest attacks would likely dim the prospects for reducing tensions in the region.