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"I can tell you that the UK is attributing responsibility with a very high degree of probability to Iran for the Aramco attacks," he said, cited by Britain's Press Association news agency on Monday.

He is due to meet with President Hassan Rouhani at the UN General Assembly in New York.

He will also discuss the attacks at a joint meeting with French President Emmanuel Macron and German Chancellor Angela Merkel.

"We think it very likely indeed that Iran was indeed responsible for using both UAVs (unmanned aerial vehicles), both drones and cruise missiles," Johnson told reporters.

"Clearly the difficulty is, how do we organise a global response? What is the way forward?

"And we will be working with our American friends and our European friends to construct a response that tries to de-escalate tensions in the Gulf region."

The United States has accused Tehran of carrying out air attacks on Saudi Arabia's Abqaiq plant and the Khurais oil field on September 14, knocking out half the kingdom's oil production.

Iran denies responsibility for the  attacks which were claimed by Iranian-back Houthi rebels in Yemen.

Johnson said: "Clearly if we are asked either by the Saudis or the Americans to have a role then we would consider in what way we could be useful.”

On Sunday, Saudi Arabia's foreign ministry said if an investigation confirmed Iran had carried out the attack on Aramco, it would be considered an “act of war”.

“We hold Iran responsible because the missiles and the drones that were fired at Saudi Arabia...were Iranian-built and Iranian-delivered,” Minister of State for Foreign Affairs Adel al-Jubeir told CNN late on Saturday.

“But to launch an attack from your territory, if that is the case, puts us in a different category... this would be considered an act of war.”

Tensions between Iran and the US and its allies have threatened to boil over since May last year when President Donald Trump unilaterally withdrew from a 2015 nuclear deal and later began reimposing sanctions in a campaign of "maximum pressure".

The tensions escalated in the wake of devastating September 14 attacks on Saudi oil installations that Washington and Riyadh have, to varying degrees, blamed on Tehran.

Following the attacks, which caused global oil prices to spike, Trump initially raised the possibility of military retaliation, tweeting that the United States was "locked and loaded".

The United States later expanded its long list of sanctions against Iran by further targeting its central bank, as Trump indicated he did not plan a military response.

US Defence Secretary Mark Esper announced on Friday that the US was sending reinforcements to Saudi Arabia at "the kingdom's request", while noting the forces would be "defensive in nature" and focused on air and missile defence.

'Stay away'

Iran's President Hassan Rouhani on Sunday denounced the presence of foreign forces in the Gulf and said Iran will proffer a peace plan, after arch-foe the United States ordered reinforcements to the region.

"Foreign forces can cause problems and insecurity for our people and for our region," Rouhani said in a televised speech at an annual military parade.

Rouhani also said Iran would present a peace plan to the United Nations in the coming days.

"In this sensitive and important historical moment, we announce to our neighbours that we extend the hand of friendship and brotherhood to them," he said.

In his speech delivered before a massive military parade on Sunday, Rouhani called on the foreign powers in the Gulf region to "stay away".

"If they're sincere, then they should not make our region the site of an arms race," he said.

"Your presence has always brought pain and misery for the region. The farther you keep yourselves from our region and our nations, the more security there will be for our region."

"We are even ready to ignore their past mistakes... since today the situation is such that the enemies of Islam and the region, meaning America and Zionism, want to abuse the rift between us.

"Our logic is the logic of a Persian Gulf whose security comes from within," said the Iranian president.

Following his speech, the Iranian armed forces paraded their latest equipment, including tanks, missiles and armoured vehicles as Rouhani and top military commanders saluted them.

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