US will 'defend' international order being 'undermined by Iran': Pentagon chief

US Defense Secretary Mark Esper said Monday that the US military is preparing a response to the attack on a major Saudi Arabia oil refinery.

After briefing President Donald Trump in the White House, Esper singled out Iran as undermining international order, without directly pinning blame on Tehran for the attack.

"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," he said in a tweet.