Britain, France, and Germany have triggered the so-called snapback mechanism of the 2015 Iran nuclear deal to reinstate UN sanctions against Tehran.
The European trio, known as the E3, wrote to the UN Security Council on August 28 to initiate the process, which takes 30 days.
In a statement, the E3 foreign ministers said, "We will use the 30-day period to continue engaging with Iran regarding our extension offer or any meaningful diplomatic efforts to restore its compliance with commitments."
They emphasized that they "share the fundamental objective that Iran must never seek, acquire, or develop a nuclear weapon."
This step puts Iran at risk of facing renewed sanctions that had been removed as part of the 2015 landmark nuclear accord, formally known as the Joint Comprehensive Plan of Action (JCPOA).
US Secretary of State Marco Rubio welcomed the E3 move.
"At the same time, the United States remains available for direct engagement with Iran -- in furtherance of a peaceful, enduring resolution to the Iran nuclear issue," he said in a statement.
"Snapback does not contradict our earnest readiness for diplomacy, it only enhances it," he added.
Iran condemned the move.
"This decision by the three European countries will seriously undermine the ongoing process of interaction and cooperation between Iran and the International Atomic Energy Agency (IAEA)," the Foreign Ministry said in a statement, calling the move a "provocative and unnecessary escalation."
Foreign Minister Abbas Aragchi said the decision was "baseless and unlawful." He added that Tehran would respond to what he called the "unjustified action," without being specific.
Later, though, Aragchi appeared more conciliatory in a letter set to EU foreign policy chief Kaja Kallas, saying Tehran is ready to restart "fair " negotiations over its nuclear program if the West shows goodwill.
He stated "Iran's readiness to resume fair and balanced diplomatic negotiations, on the condition that the other parties show seriousness and goodwill and avoid actions that harm the chances of success."
The UN called on Iran and world powers to use press forward on reaching a new nuclear deal before the snapback sanctions take effect.
"In the next 30 days, there is a window of opportunity to avoid any further escalation and find a way forward that serves peace," said Stephane Dujarric, the spokesman for UN chief Antonio Guterres.
Once the snapback process is finalized, the already-moribund JCPOA would effectively come to an end.
The deal was designed to stop the Islamic republic from developing a nuclear weapon -- something Tehran has long insisted it is not pursuing. It outlines strict rules for independent monitoring of Iran's nuclear activities and imposes caps on both the amount of uranium it can possess and the level to which it may be enriched.
Iran started to roll back its commitments after the United States withdrew from the deal in 2018 and reimposed sanctions. Iran has progressively accelerated its nuclear program since, now enriching uranium to 60 percent purity -- far above the 3.67 percent cap under the JCPOA.
Iran suspended cooperation with the International Atomic Energy Agency in July in response to the US and Israeli bombing of its key nuclear sites in Fordow, Isfahan, and Natanz. One of the conditions that the E3 had set to delay the process was for Tehran to resume full cooperation with the UN nuclear watchdog before the end of August.
