US Secretary of State Mike Pompeo (Photo: Xinhua)

US Secretary of State Mike Pompeo departed for Saudi Arabia on Tuesday to discuss possible retaliation after Washington said it had proof that attacks on Saudi oil installations originated in Iran.

Vice President Mike Pence announced that Pompeo was on his way to the kingdom 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 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 Sunday.

A US official, speaking on condition of anonymity, told AFP that the Trump administration has concluded that last weekend's attack involved cruise missiles from Iran and that evidence would be presented at the UN General Assembly next week.

The apparent hardening of the US position came as Iran's supreme leader ruled out negotiations with Washington "at any level."

This appeared to nix remaining hopes for a dramatic meeting between Trump and Iranian President Hassan Rouhani at the United Nations next week.

Speaking to reporters on Air Force One over California, Trump said he too had cooled on what had always seemed to be a diplomatic longshot.

Yemen's Huthi rebels claimed responsibility for Saturday's oil installation attacks, which halved output from the petro-state, a close ally of Washington.