Britain, France and Germany has formally accused Iran of violating the terms of its 2015 agreement to curb its nuclear program, a step by the three powers that could lead eventually to the reimposing of UN sanctions lifted under the deal.

Key points: Iran dismissed the European nations step as a "strategic mistake"

Iran dismissed the European nations step as a "strategic mistake" Russia's Foreign Ministry said activating the mechanism could make it impossible to resume implementation of the deal

Russia's Foreign Ministry said activating the mechanism could make it impossible to resume implementation of the deal British Prime Minister Boris Johnson said :"If we're going to get rid of it ... let's replace it with the Trump deal

Iran has suspended limits on its production of enriched uranium, which can be used to make reactor fuel, but also nuclear weapons.

The European powers said they were acting to avoid a crisis over nuclear proliferation adding to an escalating confrontation in the Middle East.

Russia, another signatory to the pact, said it saw no grounds to trigger the mechanism and Iran dismissed the step as a "strategic mistake".

The three countries said they still wanted the nuclear deal with Tehran to succeed and were not joining a "maximum pressure" campaign by the United States, which abandoned the pact in 2018 and has reimposed economic sanctions on Iran.

The countries triggered what is called the dispute mechanism in the deal.

Triggering the mechanism amounts to formally accusing Iran of violating the terms of the agreement.

Under the mechanism, the EU should inform the other parties — Russia and China as well as Iran — of the move.

There would then be 15 days to resolve differences, a deadline that can be extended or ultimately lead to reimposing UN sanctions.

Iran's foreign minister criticised the move.

"The usage of the dispute mechanism is legally baseless and a strategic mistake from a political standpoint," Minister Mohammad Javad Zarif said, according to the Fars news agency.

Iran, which denies its nuclear program is aimed at building a bomb, has gradually rolled back its commitments under the accord since the United States quit. It argues that Washington's actions justify such a course.

Iran's Arak heavy water nuclear facility, situated 250km south-west of Tehran. ( Fars News Agency: Mehdi Marizad, AP )

"We do not accept the argument that Iran is entitled to reduce compliance with the JCPoA," the three European countries said in a joint statement, using the formal name of the agreement, the Joint Comprehensive Plan of Action.

"Our three countries are not joining a campaign to implement maximum pressure against Iran. Our hope is to bring Iran back into full compliance with its commitments under the JCPoA," they said.

Iran has long accused the Europeans of reneging on promises to protect its economy from US sanctions.

Foreign Ministry spokesman Abbas Mousavi dismissed the "completely passive action" of the three countries.

He said Iran would support any act of "goodwill and constructive effort" to save the agreement but would give a "serious response to any destructive measures."

Russia's Foreign Ministry said activating the mechanism could make it impossible to resume implementation of the deal.

'Importance to not add to nuclear proliferation crisis'

To trigger the mechanism, the European states notified the European Union, which acts as guarantor of the agreement.

EU foreign policy chief Joseph Borrell said the aim was not to reimpose sanctions but to ensure compliance.

After months of gradual steps to reduce compliance, Iran said on January 6 it would scrap limits on enriching uranium.

The nuclear diplomacy is at the heart of a broader confrontation between Iran and the United States, in which Washington killed an Iranian general in a drone strike in Baghdad and Tehran responded by launching missiles on US targets in Iraq.

"Given recent events, it is all the more important that we do not add a nuclear proliferation crisis to the current escalation threatening the whole region," the European states said, adding that their aim was preserving the deal.

US President Donald Trump abandoned the nuclear deal reached under his predecessor Barack Obama, arguing it was too weak and new sanctions would force Iran to accept more stringent terms.

Iran gradually rolled back its commitments under the accord since the United States quit. ( Reuters: Shamil Zhumatov )

Iran says it will not negotiate with sanctions in place.

British Prime Minister Boris Johnson said on Tuesday: "If we're going to get rid of it, let's replace it and let's replace it with the Trump deal."

The US Special Representative for Iran, Brian Hook, said Washington was "very pleased" by Mr Johnson's comments.

He also said the United States would like France, Britain and Germany to join its efforts of diplomatic isolation against Tehran.

In Jerusalem, Israeli Prime Minister Benjamin Netanyahu said Israel would not allow its arch-foe Iran to obtain nuclear weapons and called on Western countries to impose "snapback sanctions" on Tehran under the previous UN resolutions.

"We know exactly what is happening with the Iranian nuclear program. Iran thinks it can achieve nuclear weapons."

"I reiterate: Israel will not allow Iran to achieve nuclear weapons," Mr Netanyahu said.

Reuters