Iran's plans to install advanced centrifuges at its main nuclear enrichment plant in Natanz are "deeply worrying," France, Germany and the UK said on Monday.

The three governments, dubbed the E3, said the plans were contrary to the 2015 Joint Comprehensive Plan of Action (JCPoA) between Tehran and world powers aiming to restrain Iran's nuclear program by barring sophisticated centrifuges.

The deal was negotiated to maintain the "peaceful nature of Iran's nuclear program" and is the "best, and currently the only, way to monitor and constrain" the program, the E3 said.

Under the terms of the nuclear deal, Iran is only meant to enrich uranium with a less sophisticated variety of centrifuges. However, US President Donald Trump withdrew from the agreement in 2018. Since May last year, Iran has taken steps to violate that limit.

The UN's nuclear watchdog, the International Atomic Energy Agency (IAEA), said last month that Iran had installed and begun operating advanced centrifuges at an underground section at Natanz.

The E3 said it has also "taken note, with great concern, for the recent law passed by the Iranian Parliament" which would "substantially expand Iran's nuclear program and limit IAEA monitoring access.

"The measures would be incompatible with the JCPoA and Iran's wider nuclear commitments," the E3 said.

A bill "for the lifting of sanctions and protection of the Iranian people's interests" was approved by the Guardian Council on Wednesday, but first has to be signed into law by President Hassan Rouhani.

Rouhani, whose government has indicated a willingness to engage with US President-elect Joe Biden, called the bill "detrimental to the course of diplomatic activities."

The E3 said that if Iran was serious about wanting to return to diplomacy with the incoming US administration, it had to reverse the bill first.

"If Iran is serious about preserving a space for diplomacy, it must not implement these steps," the governments said. "We will address Iran's non-compliance within the framework of the JCPoA."

lc/dr (AFP, Reuters)