Iran said on Tuesday it had dismantled a US spy network, after Washington announced it would deploy 1,000 more troops to the Middle East and as key powers expressed concerns about regional tensions.

Tehran's announcement came a day after it said its uranium stockpile would on June 27 surpass a limit agreed in the 2015 nuclear deal, a multilateral agreement Washington unilaterally abandoned in May last year.

Tensions between Tehran and Washington have escalated ever since, with the US bolstering its military presence in the region, reimposing sanctions and blacklisting Iran's elite Revolutionary Guards as a terrorist organisation.

“Following clues in the American intelligence services, we recently found the new recruits Americans had hired and dismantled a new network,” Iran's state news agency IRNA said, quoting an intelligence ministry official.

It said some members of the alleged CIA network had been arrested and handed over to the judiciary, while others still required “additional investigations”.

In what it termed a “wide-reaching blow” to US intelligence, IRNA said Tehran had carried out the operation in cooperation with “foreign allies”, without naming any state.

The agency's source did not specify how many agents were arrested or if they were operating only in Iran.

'Show restraint'

In Moscow, President Vladimir Putin's spokesman Dmitry Peskov on Tuesday urged all sides “to show restraint.” “We would prefer not to see any steps that could introduce additional tensions in the already unstable region,” he said.

And China's Foreign Minister Wang Yi warned all sides “not to take any actions to provoke the escalation of tension... and not to open a Pandora's box.” He urged Washington to “change its practise of extreme pressure” but also called on Tehran not to abandon the nuclear agreement “so easily.”

On Monday, Washington piled on the pressure against Iran by announcing a new troop deployment.

“I have authorised approximately 1,000 additional troops for defensive purposes”, acting Pentagon chief Patrick Shanahan said in a statement.

The United States has blamed Iran for last week's attacks on two tankers in the Gulf of Oman, an accusation Tehran denies as “baseless.” The Pentagon released new images on Monday that it said showed Iran was behind the attack on one of the ships.

The US argument centres on what it describes as an unexploded limpet mine on the Kokuka Courageous tanker ship that it says was removed by Iranians on a patrol boat.

“Iran is responsible for the attack based on video evidence and the resources and proficiency needed to quickly remove the unexploded limpet mine,” the Pentagon said in a statement accompanying the imagery.

The US released a grainy black and white video last week it said showed the Iranians removing the mine, but has not provided an explanation for why they allegedly did so while the US military was in the area.

French President Emmanuel Macron took a more circumspect line, saying that “only once all the information has been gathered and all the doubts lifted can the attributions (of blame) be made in a certain way.”

The images released on Monday show the site where the unexploded mine was allegedly attached, personnel on a patrol boat who are said to have removed the device, and damage from another device that did explode.

Tehran has vehemently denied any involvement in the attack on the Kokuka Courageous and another ship, and hinted Washington itself could be responsible.

In an interview with Time magazine, US President Donald Trump downplayed the tanker attacks, saying “So far, it's been very minor”.

Trump also said he would order military action in the event that Iran had to be prevented from getting nuclear arms, but that he was not eager for war.

“I would certainly go over nuclear weapons,” he said.

Iran ultimatum

Iran's atomic energy organisation said on Monday the country would soon pass the amount of low-enriched uranium allowed under the nuclear deal.

“The countdown to pass the 300 kilogrammes reserve of enriched uranium has started and in 10 days' time... we will pass this limit,” said spokesman Behrouz Kamalvandi.

The move “will be reversed once other parties live up to their commitments”.

President Hassan Rouhani announced on May 8 that Iran would stop observing restrictions it had agreed to in the nuclear deal, in retaliation for the US withdrawal.

Rouhani also said Iran would further scale down nuclear commitments by July 8 unless remaining parties to the deal — Britain, China, France, Germany and Russia — help it circumvent US sanctions and sell oil.

European leaders have urged Iran to stick to the deal, which set a limit on the number of uranium-enriching centrifuges, and restricted the country's right to enrich uranium to no higher than 3.67 per cent, well below weapons-grade levels of around 90 percent.