WASHINGTON — The United States has concluded that an attack on Saudi oil facilities was launched from Iran, a US official said on Tuesday as Vice President Mike Pence again warned that the US military is "locked and loaded" for a possible response.

The official, speaking on condition of anonymity, said the strike involved cruise missiles and that evidence would be presented at the UN General Assembly next week.

Pence announced that Secretary of State Mike Pompeo was on his way to Saudi Arabia to "discuss our response."

"As the president said, we don't want war with anybody but the United States is prepared," Pence said in a speech to the Heritage Foundation think tank in Washington.

"We're locked and loaded and we're ready to defend our interests and allies in the region, make no mistake about it," he said, echoing President Donald Trump's words on Monday.

Trump called off a retaliatory US missile attack on Iran in June after the Iranians shot down a spy drone. He said he did not want to kill what generals told him could be up to 150 people.

He has indicated that he may no longer feel that restraint.

"I'm not looking to get into new conflict, but sometimes you have to," he said on Monday. "That was a very large attack, and it could be met by an attack many, many times larger."

US Secretary of Defense Mark Esper labelled Iran a destabilizing force in the region, but stopped short of directly accusing Tehran over the strikes.

The US military, he said, was working with its partners to "address this unprecedented attack."

Meanwhile, Britain and Germany on Tuesday urged the international community to forge a "collective response" to the attacks.

French Foreign Minister Jean-Yves Le Drian, visiting Cairo, said it was "imperative to put all our efforts together to achieve this de-escalation".

China condemned the attacks and appealed to all sides to "refrain from taking actions that lead to an escalation of tensions in the region." — AFP