Defence Secretary Mark Esper described the deployment as a “first step” that would be “defensive in nature”.

US and Saudi officials have blamed Iran for the predawn attack by 18 explosive-laden drones and seven cruise missiles on the world’s largest oil processing facility and a nearby oilfield.

Secretary of State Michael R Pompeo on Thursday condemned what he called an “act of war” but stopped short of calling for direct retaliation.

“Attacking other nations and disrupting the global economy has a price,” Pompeo said Friday.

Trump sanctions Iran’s central bank for attack on Saudi oil facilities

Trump is expected to use his Tuesday speech at the United Nations General Assembly in New York to seek international support for confronting Tehran. His previous ability to build coalitions has been hamstrung by his open disdain for international alliances.

“The easiest thing I can do, like I could do it right in here, would say, ‘Go ahead, folks, go do it,’” Trump told reporters in the Oval Office on Friday, referring to military action. “And that would be a very bad day for Iran.”

He added: “It’s all set to go, but I’m not looking to do that if I can.”

Speaking at the Pentagon, Esper reiterated claims that Iran was behind the attack on Saudi Arabia’s oil industry.

“The weapons were Iranian produced,” he said, “and not launched from Yemen.”

Iranian-backed Houthi militants in Yemen have said they launched the attack.

Esper did not say whether the attack originated on Iranian soil, however. Saudi officials have also stopped short of publicly making that assessment.

Tehran has denied responsibility, and Iranian Foreign Minister Mohammad Javad Zarif warned on Thursday of “all-out war” if the US or Saudi Arabia launched a retaliatory strike.

China calls for calm in aftermath of drone strikes on Saudi oil facilities

In addition to deploying US troops, Esper said Washington would send more military equipment to Saudi Arabia and the neighbouring United Arab Emirates “to enhance their ability to defend themselves”.

The announcement was an implicit acknowledgement that Saudi Arabia, despite its purchase of billions of dollars in American weapons systems, was at risk of another attack from Iran without direct US involvement.

“The fact is, the Saudis were attacked by both drones and cruise missiles, and are still vulnerable to attack,” Esper said. “So asking allies and partners to contribute resources … I don’t think is too much of an ask in this situation.”

General Joseph Dunford, chairman of the Joint Chiefs of Staff, said the US would help provide “a layered system of defensive capabilities to mitigate the risk of swarms of drones or other attacks that may come from Iran”.

Tensions between the US and Iran have risen since last year, when Trump abruptly withdrew from the international nuclear accord forged by President Barack Obama in 2015.

None of the other world powers who signed the deal backed Trump, and all have tried to keep the deal alive.

Trump has sought to cripple Iran’s economy through sanctions in an unsuccessful effort to force it back to the negotiating table. Tehran has responded with its own provocations, including seizing a British oil tanker and shooting down a US reconnaissance drone this summer.

Trump recently offered to meet with Iran’s president, Hassan Rowhani, but that seems increasingly unlikely.

Both will be at the UN next week, but the Iranians have ruled out a meeting.

“We have many other military options available should they be necessary,” Esper said. “We urge the Iranian leadership to cease their destructive and destabilising activities and move forward on a peaceful, diplomatic path.”