US President Donald Trump says there are many options short of war with Iran after Saudi Arabia displayed remnants of drones and missiles it said were used in an attack on its oil sites that was “unquestionably sponsored” by Tehran.

“There are many options. There’s the ultimate option and there are options that are a lot less than that. And we’ll see,” Trump told reporters in Los Angeles.

“I’m saying the ultimate option meaning go in – war.”

The president struck a cautious note as his Secretary of State Mike Pompeo, during a visit to Saudi Arabia, described the attacks as “an act of war” on the kingdom, the world’s largest oil exporter.

Trump said on Twitter that he had ordered the US Treasury to “substantially increase sanctions” on Iran, which denies carrying out the attacks, and told reporters the unspecified, punitive economic measures would be unveiled within 48 hours.

I have just instructed the Secretary of the Treasury to substantially increase Sanctions on the country of Iran!

— Donald J. Trump (@realDonaldTrump) September 18, 2019

Trump’s tweet followed repeated US assertions that the Islamic Republic was behind Saturday’s attacks and came hours after Saudi Arabia said the strike was a “test of global will”.

Iran again denied involvement in the September 14 raids, which hit the world’s biggest crude oil processing facility and initially knocked out half of Saudi output. Saudi Arabia is the world’s leading oil exporter.

Responsibility was claimed by Yemen’s Iran-aligned Houthi group, which on Wednesday gave more details of the raid, saying it was launched from three sites in Yemen.

In a remark that may further strain a tense political atmosphere in the Gulf, the Houthis said they had listed dozens of sites in the United Arab Emirates, Riyadh’s top Arab ally, as possible targets for attacks.

U.S. President Donald Trump said, Wednesday, September 18, he has “many options” in addition to military strikes against Iran, and that details of newly announced sanctions will come within 48 hours. (AFP)https://t.co/m4rsjwJkxH pic.twitter.com/2YgB7gjChk

— The Voice of America (@VOANews) September 18, 2019

To bolster its assertion that Iran was responsible, Saudi Arabia showed drone and missile debris it said amounted to undeniable evidence of Iranian aggression.

A total of 25 drones and missiles were used in the attacks sponsored by Iran but not launched from Yemen, Defence Ministry spokesman Colonel Turki al-Malki told a news conference.

“The attack was launched from the north and unquestionably sponsored by Iran,” he said, adding Iranian Delta Wing unmanned aerial vehicles (UAV) were used in addition to cruise missiles.

An investigation into the origin of the attacks was still under way and the result will be announced later, he said.

The attack exposed gaps in Saudi air defences despite billions spent on Western military hardware.

Proof of Iranian responsibility, and evidence that the attack was launched from Iranian territory, could pressure Riyadh and Washington into a response. Both nations, however, were stressing the need for caution.

Trump has previously said he does not want war and is coordinating with Gulf and European states.

Crown Prince Mohammed bin Salman, Saudi Arabia’s de facto ruler, said the strike was a “real test of the global will” to confront subversion of the international order.

Iran dismissed the allegations.

“They want to impose maximum … pressure on Iran through slander,” Iranian President Hassan Rouhani said.

“We don’t want conflict in the region … Who started the conflict?” he added, blaming Washington and its Gulf allies for the war in Yemen.

UN officials monitoring sanctions on Iran and Yemen were heading to Saudi Arabia to investigate.

Russian President Vladimir Putin, who has offered to sell defence systems to Riyadh, called for a “thorough and impartial” probe during a phone call with Prince Mohammed.

-AAP