The International Atomic Energy Agency (IAEA) said last week that Iran had revamped its Fordo enrichment plant (FFEP), south of Tehran.

The changes would "significantly increase the rate of production of uranium enriched up to 60 percent", the agency said -- close to the 90 percent needed to make a nuclear weapon.

The rate of production will jump to more than 34 kilogrammes of highly enriched uranium per month, compared to 4.7 kilogrammes previously, it added.

The IAEA called on Iran to implement inspections urgently, while European powers pressed Tehran to "immediately halt its nuclear escalation".

"Iran agreed to the agency's request to increase the frequency and intensity of the implementation of safeguards measures at FFEP," the IAEA said in a confidential report seen by AFP.

Iran insists on its right to nuclear energy for peaceful purposes and has denied it is seeking a weapons capability.

But according to the IAEA, it is the only non-nuclear-weapon state enriching uranium to 60 percent purity.

Last month, Iran announced that it would launch "new and advanced" centrifuges in response to an IAEA board resolution that censured Tehran for its lack of cooperation with the agency.

Iran's expansion of enrichment was "a clear message that they are responding to what they feel is pressure", IAEA chief Rafael Grossi told AFP last week.

Britain, France and Germany on Tuesday "condemned" Iran's latest steps to expand its nuclear programme, "strongly urging" Tehran to reverse them.

In a letter to the UN Security Council, the three European powers raised the possibility of restoring sanctions against Iran to keep it from developing its nuclear programme.

Anouar El Anouni, the European Union foreign policy spokesman, on Friday said Iran's latest move regarding uranium production close to military enrichment levels was "extremely concerning".

Nuclear tensions between Iran and the West have simmered since Donald Trump withdrew from a landmark 2015 deal with Tehran during his first term as US president. The deal had exchanged sanctions relief for limits on Iran's nuclear programme.