FILE PHOTO: U.S. Defense Secretary Mark Esper holds a news conference with French Defense Minister Florence Parly (not pictured) at the residence of French Defense Minister in Paris, France, September 7, 2019. REUTERS/Christian Hartmann

WASHINGTON (Reuters) - U.S. Defense Secretary Mark Esper said on Monday the recent attack on Saudi Arabian oil facilities was “unprecedented” and the United States, along with its allies, was working to defend the “international rules-based order that is being undermined by Iran.”

Esper said on Twitter here he had returned to the Pentagon after a meeting at the White House, where Defense Department leadership and others briefed President Donald Trump on the situation.

Esper added that over the weekend he spoke with Saudi Arabia’s crown prince and the Iraqi minister of defense.