Sept. 14 (UPI) -- Saudi Arabia cut its oil output in half Saturday after Yemen's Houthi rebels claimed responsibility for a drone attack on two oil facilities in eastern Saudi Arabia.
A Yemeni military spokesman told the Houthi-run Al-Masirah news agency it was a "large-scale" attack with 10 drones that hit its targeted Saudi Aramco oil facilities in Abqaiq and Khurais.
The spokesman added it was a legitimate response to U.S-Saudi "aggression and siege" since 2015.
"We promise the Saudi regime to expand our operations in future and to be more painful as long as its aggression and siege continue," the spokesman said.
Saudi Arabia shut down half its oil output after the drone strikes, The Wall Street Journal reported citing unnamed sources. The shutdown will cause a loss of about 5 million barrels of oil a day, roughly 5 percent of the world's daily production of crude oil.
The kingdom typically produces 9.8 million barrels a day.
The Saudi Interior Ministry said on Twitter the drone attacks caused fires at the two facilities.
The fires were under control and authorities were investigating, the ministry tweeted.
Saudi Arabia has led a military campaign to quash the Iranian-backed Houthi rebels in Yemen since March 2015.
Though the rebels claimed responsibility, U.S. Secretary of State Mike Pompeo placed the blame squarely on Iran.
"Tehran is behind nearly 100 attacks on Saudi Arabia while Rouhani and Zarif pretend to engage in diplomacy. 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 tweeted.
"We call on all nations to publicly and unequivocally condemn Iran's attacks. The United States will work with our partners and allies to ensure that energy markets remain well supplied and Iran is held accountable for its aggression."
James Rogers, a drone and security expert and visiting research fellow at Yale University, said that the United Nations has been investigating the drones that have a range of 900 miles, which means that Houthi forces can target sites in Saudi Arabia from Yemen.
"It's quite an impressive, yet worrying technological feat," Rogers said. "Long-range precision strikes are not easy to achieve and to cause the substantial fires in Abqaiq and Khurais highlights that this drone has a large explosive yield."