Iran’s supreme leader Ayatollah Ali Khamenei has announced there will be “no negotiations on any level” with US officials, in remarks aimed at dousing speculation of a possible summit between Donald Trump and Hassan Rouhani on the sidelines of the UN general assembly next week.

As chances of any such diplomatic breakthrough dwindled, Washington announced that the secretary of state, Mike Pompeo, would leave on Tuesday night for Jeddah for talks with the Saudi crown prince, Mohammed bin Salman, to discuss Saturday’s attacks on Saudi oil installations.

The state department said it would “coordinate efforts to counter Iranian aggression in the region”.

Pompeo is then due to fly to Abu Dhabi to see Sheikh Mohammed bin Zayed of the United Arab Emirates, which has backed the Saudi proposal of a UN inquiry to identify the perpetrators of the attacks.

Both Saudi and US officials have said they believe Iranian weapons were involved in the attack, and the US media has quoted unnamed US sources as saying the air strikes were launched from southern Iran and involved a salvo of cruise missiles.

But the French foreign minister, Jean-Yves le Drian, said he had no information on who was responsible. The German chancellor, Angela Merkel, following a call with the prime minister, Boris Johnson, stressed the need to avoid further escalation.

The foreign secretary, Dominic Raab, has confined himself to condemning the attack and saying he is working to prepare a coordinated international response. That is likely to come at the UN general assembly next week, where world leaders including the Iranian president Hassan Rouhani, Trump and the French president, Emmanuel Macron, will all give speeches.

The departure of the US national security adviser, John Bolton, an advocate of forceful anti-Iran policies, from the White House last week, along with the scheduled arrival of Rouhani in New York, had raised a faint possibility of renewed high-level talks between the two countries after months of escalating threats and military posturing.

Trump appeared less keen for such a meeting in the wake of the weekend attack.

“I never rule anything out, but I prefer not meeting him,” he told reporters on the way to a political rally on Tuesday.

Speaking on the same day, the vice-president, Mike Pence, said the US was still considering its options

“We’re evaluating all the evidence. We’re consulting with our allies. And the president will determine the best course of action in the days ahead,” Pence said. “But I promise you, under President Donald Trump, America will maintain our energy dominance. And the United States of America will take whatever action is necessary to defend our country, our troops and our allies in the Gulf. You can count on it.”

Facebook Twitter Pinterest A satellite image showing damage to the Khurais oil field in Saudi Arabia. Photograph: HO/AFP/Getty Images

Tehran had consistently said that it would only hold talks if the US lifted sanctions imposed since Trump left the 2015 nuclear deal. In remarks posted on his official website on Tuesday, Khamenei, Iran’s highest authority, restated that position in blunt terms.

“If America takes back its words and repents and returns to the nuclear deal, which they have violated, they can take part in the meetings of signatories to this agreement with Iran,” Khamenei said. “Otherwise, no negotiation on any level will happen between officials of the Islamic Republic and America, neither in New York nor anywhere else.”

Q&A What is the Iran nuclear deal? Show Hide In July 2015, Iran and a six-nation negotiating group reached a landmark agreement known as the Joint Comprehensive Plan of Action that ended a 12-year deadlock over Tehran’s nuclear programme. The deal, struck in Vienna after nearly two years of intensive talks, limited the Iranian programme, to reassure the rest of the world that it cannot develop nuclear weapons, in return for sanctions relief.

At its core, the JCPOA is a straightforward bargain: Iran’s acceptance of strict limits on its nuclear programme in return for an escape from the sanctions that grew up around its economy over a decade prior to the accord. Under the deal, Iran unplugged two-thirds of its centrifuges, shipped out 98% of its enriched uranium and filled its plutonium production reactor with concrete. Tehran also accepted extensive monitoring by the International Atomic Energy Agency (IAEA), which has verified 10 times since the agreement, and as recently as February, that Tehran has complied with its terms. In return, all nuclear-related sanctions were lifted in January 2016, reconnecting Iran to global markets. The six major powers involved in the nuclear talks with Iran were in a group known as the P5+1: the UN security council’s five permanent members – China, France, Russia, the UK and the US – and Germany. The nuclear deal is also enshrined in a UN security council resolution that incorporated it into international law. The 15 members of the council at the time unanimously endorsed the agreement. On 8 May 2018, US president Donald Trump pulled his country out of the deal. Iran announced its partial withdrawal from the nuclear deal a year later. Saeed Kamali Dehghan, Iran correspondent

Since pulling out of the 2015 nuclear agreement last year, the US has imposed a policy of maximum economic pressure on Tehran, including a commitment to drive Iranian oil exports to zero.

But Trump appears determined to ensure that Saudi Arabia takes a leading role in any military response, a move that has led some security experts to suggest the US, no longer a net importer of oil, is unwilling to act automatically as the security guarantor for Saudi Arabia.

On Tuesday, the Saudi energy minister said its oil output would be back to normal by the end of the month, claiming that half the production lost in the attack had already been restored.

Prince Abdulaziz bin Salman, who was appointed to the role earlier this month, refused to be drawn on who was responsible for the strikes. “We don’t know who is behind the attack,” he said, adding that the kingdom wants “proof based on professionalism and internationally recognised standards”.

He insisted the sale of Aramco – Saudi Arabia’s state-owned oil group – would continue as planned, adding that the Saudis had large oil reserves that it could draw upon to supply the market if necessary.

But Pierre Noël, an energy specialist at the International Institute for Strategic Studies, said: “The Saudis lost in 30 minutes the war for which they had been preparing for 30 years. Saudi Arabia lost 50% of their output due to Iran or its Iranian supporters.

“It has happened without a war being waged, and crucially for Saudi Arabia without the US offering immediately an umbrella or delivering on what everyone expects since the 1970s that it would act as the guarantors of Saudi Arabian oil integrity. So we are talking about a major shift in Middle East oil geopolitics.”

He added: “The timing from the Iranian perspective was brilliant since if Trump goes to war with Iran, the oil security crisis could have potentially quite dramatic macro-economic circumstances that could badly endanger the Trump re-election campaign. But if the US does not go to war, Saudi Arabia is humiliated.

“The impact on the Aramco sale is incredible. How can you put an asset on a market that is incapable of protecting its physical integrity and is so dramatically exposed to single acts of war?”

Kori Schake, the deputy director at the International Institute for Strategic Studies, said: “This is the destruction of Mohammed bin Salman’s strategy. What kind of foreign investment are you going to draw? He banked heavily on a personalised relationship with the Trump administration.”

In the past four months, at least 13 oil tankers in the Gulf and the strait of Hormuz have been seized by Iranian forces or been targeted by acts of sabotage, starting on 12 May with the appearance of large holes in the hulls of four ships docked in Fujairah, one of the United Arab Emirates. The US and Saudi Arabia have repeatedly accused Iran of perpetrating the damage. Tehran denies the allegations.