In the wake of the drone strikes, world powers worried about a possible new war in the Middle East as Saudi Arabia said it had “undeniable” evidence Iran sponsored the attack, which took half the kingdom’s full oil-producing capacity offline, though the output has since been partially restored.

Iran on Wednesday privately and publicly warned it would respond militarily to any attack by the US and its allies, dispatching a note to Washington through the Swiss embassy in Tehran denying responsibility for the attack.

“This attack was not Iran’s doing, and claims by Donald Trump and Mike Pompeo, the president and secretary of state of America respectively, are rejected and condemned,” Iran reportedly said in a letter, according to Iranian state TV.

“Iran will immediately respond” to any threat, said the note, with a response which “will not be limited to the origin of threat”.

Separately, Iran’s official news agency reported that Iranian president Hassan Rouhani and foreign minister Mohammad Javad Zarif may not attend the UN General Assembly in New York beginning later this week as they had yet to receive visas from the US, further dimming the prospect of a diplomatic solution to the crisis.

Attack on major oil facilities in Saudi Arabia: In pictures Show all 10 1 /10 Attack on major oil facilities in Saudi Arabia: In pictures Attack on major oil facilities in Saudi Arabia: In pictures Smoke billows from multiple fires at the Aramco oil processing facility in Abqaiq, Saudi Arabia on 14 September Reuters Attack on major oil facilities in Saudi Arabia: In pictures Thick black smoke billows from a fire following drone strikes on major oil facilities in Abqaiq, Saudi Arabia Planet Labs Inc/Reuters Attack on major oil facilities in Saudi Arabia: In pictures The Aramco oil processing facility in Abqaiq, Saudi Arabia prior to the drone strikes on 14 September AP Attack on major oil facilities in Saudi Arabia: In pictures Damage is seen to the Aramco oil processing facility in Abqaiq, Saudi Arabia following drone strikes on 14 September, the previous day (Image 1 of 2) AP Attack on major oil facilities in Saudi Arabia: In pictures Damage is seen to the Aramco oil field in Abqaiq, Saudi Arabia following drone strikes on 14 September, the previous day (Image 2 of 2) AP Attack on major oil facilities in Saudi Arabia: In pictures Damage is seen to the Aramco oil field in Khurais, Saudi Arabia following drone strikes on 14 September, the previous day (Image 1 of 2) AP Attack on major oil facilities in Saudi Arabia: In pictures Damage is seen to the Aramco oil field in Khurais, Saudi Arabia following drone strikes on 14 September, the previous day (Image 2 of 2) AP Attack on major oil facilities in Saudi Arabia: In pictures Smoke billows from multiple fires following drone strikes on major oil facilities in Abqaiq, Saudi Arabia AFP/Getty Attack on major oil facilities in Saudi Arabia: In pictures Smoke rises from a fire following a drone strike at the Aramco facility in Abqaiq, Saudi Arabia on 14 September Reuters Attack on major oil facilities in Saudi Arabia: In pictures Smoke is seen following a fire at the Aramco oil processing facility in Abqaiq, Saudi Arabia on 14 September Reuters

The attack on the petroleum processing facility in the eastern Saudi city of Abqaiq raised world oil prices and threatened a global economy that some experts have warned was already teetering on the brink of another slowdown. In Turkey, for example, petrol and diesel prices jumped significantly, on news of delayed deliveries.

The attacks also showed what security experts have described as alarming new precision military capabilities by Iran and its allies in the region, potentially changing the strategic calculations in the volatile Middle East.

The US has long been committed to protecting world energy supplies and markets. The Trump administration is also closely allied with the Saudi royal circle.

Washington’s decision last year to pull out of the nuclear deal and impose crippling sanctions on Iran sparked the months-long crisis in the Gulf, with Iran vowing to exact a cost from the US and its allies for what it has described as economic warfare against the country.

Mr Trump has frequently employed sanctions as his preferred tool to punish countries that cross the US. It remains unclear what effects the latest sanctions would have since Iran is already largely cut off from conventional commercial channels.

“I have just instructed the Secretary of the Treasury to substantially increase Sanctions on the country of Iran!” he wrote in a tweet on Wednesday.

Although top US officials have accused Iran of being behind the attack, Yemen’s Houthi rebels claimed responsibility for the pinpoint targeting of the facility as a part of their four-and-a-half-year war against Saudi Arabia.

Key Washington hawks in and out of government have demanded airstrikes on Iranian targets. But Iran has warned it would respond militarily to any attack.

“We are fully prepared to act against any moves attacking our country or the interests of the Islamic Republic, and will respond to possible mischief in such a decisive and comprehensive manner that will be a big surprise for the aggressors,” Ali Shamkhani, secretary of Iran’s Supreme National Security Council, was quoted as saying by the Mehr news agency.

Veto-wielding UN Security Council members Russia and China, along with the European Union, have called for restraint on all sides, with Moscow urging the US not to make any “hasty conclusions” about the attack.

Evidence presented so far by the US has shown unexpected sophistication but failed to prove the contention that the attacks originated in Iran or from bases of Iranian-backed armed groups in Iraq. Saudi television said a defence official would present evidence later specifying Iran’s role in the attack and detailing weapons used in the attacks.

Riyadh on Wednesday displayed remnants of drones and missiles, which it said were produced in Iran in 2019, that it said were used in the weekend attacks on its oil facilities.

Donald Trump on Iran: 'I don't want a war but US is more prepared than any country'

Defence Ministry spokesman Colonel Turki al-Malki said Iranian Delta Wing unmanned aerial vehicles were used in addition to cruise missiles. “The attack was launched from the north and unquestionably sponsored by Iran,” he told a news conference.

Saudi crown prince Mohammed bin Salman, the de facto ruler of the oil-rich desert kingdom, has been scrambling to build international support. On Wednesday he telephoned Russian president Vladimir Putin, who “called for a thorough and objective investigation of the events”, according to a Kremlin announcement.

“What happened represents a real test of the international will to confront acts of sabotage that threaten international security and stability,” Prince Mohammed was quoted as saying during a conversation with South Korean president Moon Jae-in.

In a cabinet meeting on Wednesday morning, Mr Rouhani, Iran’s president, urged Saudi Arabia to end its war in Yemen, which has been described as the worst humanitarian crisis in the world.

“They struck a certain point,” he said. “They did not strike a hospital. They did not strike a school. They did not strike a market. They attacked an industrial centre in order to warn you. Learn from this warning and think about ending the war in the region.”

European officials who have traditionally sided with the US on crucial security matters appeared in no mood to sign on to any action against Iran, and have voiced alarm about the prospects of armed conflict.

“It is very close to war,” Norbert Roettgen, chair of the German parliament’s foreign affairs committee, said in a televised interview. “However, neither Iran nor the United States or Saudi Arabia are interested in a war.”