Colonel Turki Bin Saleh Al-Malki displays pieces of what he said were Iranian cruise missiles and drones in Riyadh. AFP

Saudi Arabia alleged on Wednesday an attack by drones and cruise missiles on the heart of the kingdom's oil industry was "unquestionably sponsored by Iran," naming but not directly accusing Tehran of launching the assault. Iran denies being involved in the attack claimed by Yemeni rebels, and has threatened the US that it will retaliate "immediately" if Tehran is targeted in response.

The news conference by Saudi military spokesman Col. Turki al-Malki comes after a summer of heightened tensions between Iran and the US over President Donald Trump unilaterally withdrawing America from Tehran's 2015 nuclear deal with world powers.

Al-Malki made a point not to directly accuse Iran of firing the weapons or launching them from inside of Iranian territory. The kingdom has sought help from international investigators and the United Nations, both lengthening the probe and internationalizing its conclusions.

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"The attack was launched from the north and was unquestionably sponsored by Iran," Al-Malki told journalists.

The news conference took place with a backdrop of broken and burnt drones and pieces of one cruise missile allegedly collected from the attacks.

Al-Malki described the drones as "delta wing" models, which looked like large triangles. The cruise missile, which al-Malki described as a "Ya Ali" type, had a small jet engine attached to it.

Eighteen drones and seven cruise missiles were launched in the assault, Al-Malki said, with three missiles failing to make their targets. He said the cruise missiles had a range of 700 kilometers (435 miles), meaning they could not have been fired from inside Yemen. He played surveillance video he said showed a drone coming in from the north. Satellite images released earlier by the US showed damage largely on the north-facing sides of structures at the sites.

"This is the kind of weapon the Iranian regime and the Iranian IRGC are using against the civilian object and facilities infrastructure," he said, using an acronym for Iran's paramilitary Revolutionary Guard.

He added: "This attack did not originate from Yemen, despite Iran's best effort to make it appear so."

Iran sent a note to the US via Swiss diplomats in Tehran on Monday, reiterating that Tehran denies being involved in the Saudi attack, the country's state-run IRNA news agency reported. The Swiss have looked after American interests in Tehran for decades.

"If any action takes place against Iran, the action will be faced by Iran's answer immediately," IRNA quoted the note as saying. It added that Iran's response wouldn't be limited to the source of the threat, suggesting it would inflict damage beyond what it had suffered.

IRNA separately reported Wednesday that Iran's first delegation for the annual UN General Assembly meeting had not left Iran because the US has yet to issue them visas. Foreign Minister Mohammad Javad Zarif was to travel to New York on Friday, with Iranian President Hassan Rouhani following Monday, according to the agency. The UN meeting had been considered as an opportunity for direct talks between Rouhani and Trump.

Tehran has denied involvement in the Sept. 14 attacks on oil plants, including the world's biggest crude processing facility, that initially knocked out half of Saudi Arabia's production.

Yemen's Houthi group, an ally of Iran, has claimed responsibility and said they used drones to assault state oil company Aramco's sites.

The Custodian of the two Holy Mosques King Salman Bin Abdulaziz Al Saud chaired the cabinet's session at Al-Salam Palace in Jeddah on Tuesday afternoon.

At the outset of the session, the King expressed thanks and appreciation to the leaders of countries, officials of states, regional and international organisations and all those who expressed condemnation of the sabotage attack on two Aramco plants in Abqaiq and Khurais, reaffirming the Kingdom's ability to deal with the effects of such cowardly attacks which do not only target vital installations of the Kingdom, but also target global oil supplies and threaten the stability of the global economy.

Secretary of State Mike Pompeo and other US officials were headed to Saudi Arabia. United Nations experts monitoring sanctions on Iran and Yemen also left for the kingdom, Saudi's UN envoy told the media.

Concrete evidence showing Iranian responsible, if made public, could pressure Riyadh and Washington into a response, though US President Donald Trump said he does not want war.

The Saudi Defence Ministry said it will hold a news conference on Wednesday (today) at 1430 GMT to present "material evidence and Iranian weapons proving the Iranian regime's involvement in the terrorist attack.” Riyadh has already said preliminary results showed the attack did not come from Yemen.

A US official told the media the strikes originated in southwestern Iran. Three officials said they involved cruise missiles and drones, indicating a higher degree of complexity and sophistication than initially thought.

This satellite overview courtesy of the US Government shows damage to oil/gas infrastructure in Saudi Arabia. AFP

The officials did not provide evidence or explain what US intelligence they were using for the evaluations.

Some US allies, as well as those of Iran, have asked for proof behind accusations Tehran was responsible for the attack that cut 5 per cent of global production. Saudi Arabia, the world's top oil exporter, said on Tuesday the 5.7 million barrels per day of output would be fully restored by the end of the month.

Oil prices fell after the Saudi reassurances, having surged more than 20 per cent at one point on Monday — the biggest intra-day jump since the 1990-91 Gulf War.

Illustrating international caution on such an inflammatory issue, Japan's new defence chief said Tokyo has not seen any intelligence that shows Iran was involved.

“Compelling” evidence

A senior US official called for a UN Security Council response to the attacks, although success is unlikely because diplomats say Russia and China — who have veto powers — are likely to shield Iran.

US Secretary of State Mike Pompeo gets ready to board for Saudi Arabia and the United Arab Emirates. Reuters

One of the three US officials voiced confidence the Saudi probe would yield "compelling forensic evidence" determining the origins of the attack that has exposed serious gaps in Saudi air defences despite billions of dollars spent on Western military hardware.

Saudi UN Ambassador Abdallah Al Mouallimi told the media the experts monitoring sanctions on Iran and Yemen were heading to Saudi Arabia along with those from a separate independent panel who also report to the Security Council.

France is also to send experts in response to a request from Saudi Arabia's crown prince.

The situation could harm French diplomacy meant to avert a feared US-Iranian conflict, diplomats told the media after Macron's top envoy held talks in Saudi Arabia.

Iran's Supreme Leader Ayatollah Ali Khamenei ruled out talks with the United States unless it returns to the nuclear accord between Iran and the West that Washington quit last year.

Trump said on Monday there was "no rush" to retaliate and Washington was coordinating with Gulf Arab and European states.

Already frayed US-Iran ties deteriorated further when Trump quit the nuclear pact and reimposed sanctions, severely hurting the Iranian economy.

Washington and its Gulf Arab allies also want Iran to stop supporting regional proxies, including the Houthis who have been battling a Saudi-led military coalition in Yemen for four years.

Despite years of air strikes against them, the Houthi movement boasts drones and missiles able to reach deep into Saudi Arabia, the result of an arms race since the Western-backed, Sunni Muslim coalition intervened in Yemen against the group in March 2015.

Iran's clerical rulers support the Houthis, but Tehran denies it actively supports them with military and financial support. In Wednesday's video carried by Iran's media, Rouhani said the oil attack was a "warning" by Yemenis.

Maritime coalition

Wednesday's announcements comes after Saudi Arabia's energy minister said late Tuesday that more than half of the country's daily crude oil production that was knocked out by an attack had been recovered and that production capacity at its targeted plants would be fully restored by the end of the month.

Saudi Energy minister Prince Abdulaziz Bin Salman is pictured during a news conference in Jeddah. Reuters

"Where would you find a company in this whole world that went through such a devastating attack and came out like a phoenix?" Energy minister Prince Abdulaziz bin Salman said about state-owned Saudi Aramco, which was the target of the attacks. His question to reporters, many of them Saudi, drew applause.

Prince Abdulaziz said Aramco will honor its commitments to its customers this month by drawing from its reserves of crude oil and offering additional crude production from other oil fields. He said production capacity would reach up to 11 million barrels a day by the end of September and 12 million barrels in November.

He said production at the Abqaiq processing facility is currently at 2 million barrels per day.

Oil prices spiked Monday, with benchmark Brent crude having the biggest percentage gain since the 1991 Gulf War. Prices dropped Tuesday around the Saudi announcement. Brent traded Wednesday morning around the same prices as the day before, with a barrel costing over $64.

Agencies