Iran's supreme leader Ayatollah Ali Khamenei Photo: VCG

Iran's supreme leader Ayatollah Ali Khamenei on Tuesday ruled out negotiations with the US, as tensions mount between the arch-foes after Washington blamed Tehran for attacks on Saudi oil installations.

"The policy of 'maximum pressure' against the Iranian nation is worthless and all Islamic Republic of Iran officials unanimously believe there will be no negotiations with the US at any level," he said, quoted on his official website.

Tehran and Washington have been at loggerheads since May last year when US President Donald Trump withdrew from a 2015 nuclear deal and began reimposing crippling sanctions in a campaign of "maximum pressure."

Iran responded by scaling back its commitments under the landmark accord, which gave it the promise of sanctions relief in return for limiting the scope of its nuclear programme.

The US said on Monday that its military was readying a response to the "unprecedented" weekend attacks on Saudi oil facilities.

Trump said the US was ready to help its key ally Saudi Arabia after the attacks that triggered a record leap in world oil prices.

"I'm not looking to get into new conflict, but sometimes you have to," he said. "That was a very large attack, and it could be met by an attack many, many times larger... Certainly, it would look to most like it was Iran," Trump said.

US Secretary of Defense Mark Esper also singled out Iran as a regional destabilizing force, while stopping short of directly accusing Tehran over the strike.

The US military, he said, was working with its partners to "address this unprecedented attack and defend the international rules-based order that is being undermined by Iran."

A day after the attacks, the White House had said Trump could meet his Iranian counterpart Hassan Rouhani on the sidelines of the United Nations General Assembly in New York next week.

But Khamenei said any talks with the Americans would lead to the "imposition of their demands on Iran" and mean their policy of "maximum pressure" was a success.

Speaking to students, he said that was the reason why Rouhani, Foreign Minister Mohammad Javad Zarif and other officials "unanimously declared we won't negotiate with US bilaterally or multilaterally."