France, Germany and Britain voiced grave concern on Thursday about a report that Iran had accelerated its enrichment of uranium to near weapons-grade, saying this was a serious violation of its commitments.
At a time when the West and Iran are looking to resume talks on reviving a nuclear deal, the UN atomic energy watchdog said in a report seen by Reuters that Iran had accelerated its enrichment of uranium.
In a joint statement, the three countries said they were worried about IAEA reports confirming that Iran has produced uranium metal-enriched up to 20% fissile purity for the first time and lifted production capacity of uranium enriched to 60%.
Both are key steps in the development of a nuclear weapon, they said.
Uranium metal can be used to make the core of a nuclear bomb, but Iran says its aims are peaceful and it is developing reactor fuel.
"Iran must halt activities in violation of the Joint Comprehensive Plan of Action (JCPoA) without delay," said the joint statement from the three foreign ministries.
"We urge Iran to return to the negotiations in Vienna as soon as possible with a view to bringing them to a swift, successful conclusion. We have repeatedly stressed that time is on no-one's side," they added.
The accelerated enrichment is the latest move by Iran breaching restrictions imposed by a 2015 nuclear deal, which capped the purity to which Tehran can refine uranium.
The United States and its European allies have said such moves threaten talks on reviving the deal, which is currently suspended.