TEHRAN: A top Iranian diplomat expressed disappointment on Sunday after meeting a minister from Britain's Foreign Office amid escalating regional tensions, saying the talks were "repetitive", state news agency IRNA reported.

Minister of State for the Middle East Andrew Murrison had the "usual talking points", said  Kamal Kharazi, the head of the Strategic Council of Foreign Relations at Iran's Foreign Ministry.

These included saying a European payment mechanism to help Iran with US sanctions "will soon become operational, that Britain has always supported the JCPOA and has its own problems with America ... such talks that have always been repetitive," Kharazi added.

The JCPOA is the Joint Comprehensive Plan of Action, a multilateral 2015 nuclear deal that the US unilaterally withdrew from in May last year.

Washington has since re-imposed biting sanctions against the Islamic Republic, despite Britain, China, France, Germany and Russia remaining committed to the deal.

Murrison is expected to meet deputy foreign minister Abbas Araghchi later on Sunday.

Murrison was to call for an "urgent de-escalation" and raise British concerns "about Iran's regional conduct and its threat to cease complying with the nuclear deal", according to a statement by Britain's Foreign Office.

Tensions between Washington and Tehran have flared further after Iran on Thursday shot down a US drone.

Iran said the drone violated its airspace -- a claim the US denies -- near the strategic Strait of Hormuz.

In response, the US was ready to carry out a military strike against Iran but US President Donald Trump said he called it off at the last minute.

The downing of the drone came after tensions spiked between the two countries following a series of attacks on commercial vessels that the US has blamed on Iran -- accusations vehemently denied by the Islamic Republic.

Britain is a signatory to the 2015 nuclear deal which saw Iran scale back its nuclear programme in exchange for sanctions relief.

Europe has tried to respond to the US withdrawal by setting up a special trade mechanism called INSTEX that would allow legitimate trade with Iran to continue without falling foul of US sanctions.

But the mechanism has been dismissed by Iran's Supreme Leader Ayatollah Ali Khamenei as a "bitter joke."

On May 8, Iran said it would reduce some of its nuclear commitments unless the remaining partners helped it circumvent US sanctions and sell its oil.

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

The deal set a limit on the number of uranium-enriching centrifuges, and restricted Iran's right to enrich uranium to no higher than 3.67 percent, well below weapons-grade levels of around 90 percent.

Kharazi warned Sunday that European powers must realise Iran is "serious" about its decision and that "in two weeks it will take new steps" to scale down nuclear commitments.—AFP