The three allies said Iran's moves were undermining a landmark 2015 deal on its nuclear programme, after the International Atomic Energy Agency (IAEA) on Thursday said the country was strengthening enrichment facilities at two sites.

"These measures will again increase Iran's stock of enriched uranium and enrichment capacity, whose levels have already surpassed the limits set" by the 2015 deal, the French, German and British foreign ministries said in a joint statement.

The condemnation came more than a week after the countries tabledt a resolution at an IAEA board of governors meeting criticising Tehran's lack of cooperation with the nuclear watchdog, the first such move since November 2022.

Iran condemned the resolution as "hasty and unwise".

It denies seeking to develop a nuclear weapon, saying its atomic programme is for peaceful and civilian purposes.

Germany, France and Britain said it was unacceptable that Iran presented its measures as a reaction to the resolution.

They reiterated their commitment to a diplomatic solution preventing Tehran developing a nuclear weapon.

According to the IAEA, Iran is the only non-nuclear weapon state to enrich uranium to the high level of 60 percent -- just short of weapons-grade -- while it continues accumulating large uranium stockpiles.

The IAEA has said Tehran has significantly ramped up its nuclear programme and now has enough material to build several atomic bombs.

The Islamic republic has gradually broken away from its commitments under the 2015 deal it struck with world powers.

The accord provided relief from Western sanctions in exchange for curbs on Iran's atomic programme.

It fell apart after the unilateral withdrawal of the United States under then-president Donald Trump in 2018.

Efforts to revive the deal have so far failed.