Secretary of State Mike Pompeo has blamed Iran for a drone attack on a Saudi Arabian oil refinery that has crippled the country’s oil production. In a series of posts on Twitter, he claimed Iran was behind the attack on the Saudi plant at Abqaiq, and said the U.S. will work with the Saudis on an appropriate response. “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,” Pompeo wrote. The secretary of state placed blame for the attack directly on Iran rather than Iran-backed Houthis in Yemen, who had launched several previous drone attacks on the Saudis. Oil processing in the country has been cut in half since the attack on the plant, which is the largest crude oil processing facility in the world.