U.S. Secretary of State Michael Pompeo blamed Iran for attacks on a massive Saudi Aramco oil facility, saying there was no evidence the drones originated in Yemen as Tehran-backed rebels there claimed.

Iran denied responsibility for the attacks, which forced Saudi Arabia to cut its daily oil output in half.

Pompeo tweeted after the White House confirmed that President Donald Trump offered support for Saudi Arabia’s self-defense in a call on Saturday with Saudi Crown Prince Mohammed Bin Salman.

Iran launched an “unprecedented attack on the world’s energy supply,” Pompeo said on Twitter after at least one Republican lawmaker urged the U.S. to respond in kind with a strike on Iranian oil facilities.

Pompeo said the U.S. will work with allies to ensure the energy market remains well supplied, echoing comments from the White House. He also called on all nations to “publicly and unequivocally condemn Iran’s attacks.”

Iranian Foreign Ministry spokesman Abbas Mousavi rejected the U.S. allegations, saying such “blind and fruitless accusations and statements are unfathomable and meaningless.” Foreign Minister Mohammad Javad Zarif tweeted, “Having failed at ‘max pressure,’ @SecPompeo’s turning to ‘max deceit.’”

Iranian-backed Houthi rebels in Yemen claimed responsibility for the strikes. A Saudi-led coalition backed by the U.S. has been fighting for more than four years to try to vanquish the Houthis and restore Yemen’s President Abdrabbuh Mansour Hadi to power.

The U.S. “strongly condemns today’s attack on critical energy infrastructure,” White House spokesman Judd Deere said in an emailed statement that was also posted on Twitter. The U.S. government “is monitoring the situation and remains committed to ensuring global oil markets are stable.”

Republican Senator Lindsey Graham, a confidant of Trump, earlier urged a decisive U.S. response against Iranian targets.

“It is now time for the U.S. to put on the table an attack on Iranian oil refineries if they continue their provocations or increase nuclear enrichment,” Graham of South Carolina said on Twitter. “Iran will not stop their misbehavior until the consequences become more real, like attacking their refineries.”