Britain, France, Germany and US said after talks based in Paris that they were "united in underlining the dangerous nature of a decision to limit IAEA access" ahead of a February 21 deadline set by the Iranian parliament.

French Foreign Minister Jean-Yves Le Drian hosted his German and British counterparts in Paris, with America's new Secretary of State Antony Blinken joining via videoconference.

Their statement urged "Iran to consider the consequences of such grave action, particularly at this time of renewed diplomatic opportunity", adding that they all shared the aim of Iran returning to "full compliance" with the accord.

Analysts say only a small window of opportunity remains to save the deal, which received a near-fatal blow when former US president Donald Trump walked out of the accord in 2018 and reimposed sanctions on Iran.

The administration of US President Joe Biden has said it is prepared to rejoin the deal and start lifting sanctions if Iran -- whose economy has been devastated -- returns to full compliance.

Iran has warned it would restrict some UN nuclear agency inspections by February 21 if the US does not lift the sanctions imposed since 2018.

Blinken reiterated that if "Iran comes back into strict compliance with its commitments" under the nuclear deal "the United States will do the same and is prepared to engage in discussions with Iran toward that end."

The powers also expressed their concerns over Iran's recent actions to produce both uranium enriched up to 20 percent and uranium metal in new violations of the accord.

"These activities have no credible civil justification," the statement said, adding: "Uranium metal production is a key step in the development of a nuclear weapon."