Earlier, US officials including President Donald Trump accused Iran of being responsible for Saturday's attacks on two major Saudi oil facilities. Tehran has dismissed the accusations. The Houthis, a Yemeni militia group against which Riyadh and its allies have waged a four year war, claimed responsibility and promised more attacks.

The US is "locked and loaded" prepared to respond to the "Iranian" attack on Saudi Arabia's oil fields, US Vice President Mike Pence has announced.

"In the wake of this weekend's unprovoked attack on several oil facilities in Saudi Arabia, I promise you, we're ready," Pence said, speaking at a Heritage Foundation event in Washington, DC on Tuesday.

"As the president said, we don't want war with anybody. But the United States is prepared, we're locked and loaded, and we're ready to defend our interests and our allies in the region. Make no mistake about it," Pence said.

Reiterating Trump's claim Monday that was 'looking like' Iran was behind the attacks, Pence said the US intelligence community, "at this very hour, is working diligently to review the evidence," with Secretary of State Mike Pompeo heading to Riyadh "to discuss our response."

According to Pence, if Iran was behind the attacks, it would be just "the latest in a series of increasingly dangerous escalations instigated by the Islamic Republic."

Praising on the Trump administration's recent success in securing $738 billion for the US military, the vice president said that America's "active duty personnel are now the best equipped, best trained and most technologically advanced fighting force in the history of the world."

Pence's comments follow a series of statements by US officials including President Trump accusing Iran of attacking Saudi Aramco's oil fields on Saturday.

Earlier Tuesday, an anonymous US official told AFP that the US was now certain that the attack was launched from Iranian soil, and involved the use of cruise missiles.

Tehran has refuted US and Saudi claims about its involvement, but defended Yemen's right to "protect themselves from [Saudi] attacks."

The Houthis, a rag-tag Yemeni militia group against which Saudi Arabia and its allies are waging a war, claimed responsibility for Saturday's attacks, and said Saudi efforts to blame others were a sign of "cowardice." The group has launched dozens of attacks against Saudi infrastructure and military facilities in recent years using small drones and ballistic missiles.