Defense Secretary Mark Esper said Monday that he had spoken with Saudi Crown Prince Mohammed bin Salman and Iraq's minister of defense about the drone attack on Saudi Arabia's oil supply over the weekend.
Esper also said on Twitter that President Donald Trump had been briefed by U.S. Defense leaders and other officials at the White House on Monday.
"The United States military, with our interagency team, is working with our partners to address this unprecedented attack and defend the international rules-based order that is being undermined by Iran," Esper tweeted.
Esper's statements came as tensions between the U.S. and Iran reached new highs. Secretary of State Mike Pompeo quickly blamed Tehran for the attack, while Trump said his administration has "reason to believe that we know the culprit."
The U.S. is "locked and loaded depending on verification," Trump tweeted Sunday, and is "waiting to hear from the Kingdom as to who they believe was the cause of this attack, and under what terms we would proceed!"
Iran has denied any responsibility for the attacks. Yemen's Houthi rebels, which are backed by Tehran, claimed responsibility for the drone strikes.
But Pompeo tweeted Saturday that "there is no evidence the attacks came from Yemen."
The attacks over the weekend struck at the heart of the Saudi kingdom's oil-making facilities and raised fears about the security of Middle Eastern crude.
The oil processing facilities at Abqaiq and the nearby Khurais oil field were attacked, knocking out 5.7 million barrels of daily crude production — about half of the kingdom's oil output. That translates to about 5% of global daily oil production.
Brent crude futures shot up Monday, clocking record gains of up to 19.5% at their peak. The contract closed the session up 14.6% at $69.02.
This is a developing story. Please check back for updates.