Officials from Britain, France, Germany, China and Russia will meet Iranian delegates on December 6, two weeks after the UN nuclear watchdog demanded Tehran explain the presence of uranium particles at an undeclared site near Tehran.

The 2015 agreement to curb Tehran's nuclear activities is in a parlous state, faltering since US President Donald Trump pulled out last year and reimposed swingeing sanctions, prompting Iran to breach some parts of the deal in response.

"A meeting of the Joint Commission of the Joint Comprehensive Plan of Action (JCPoA) will take place in Vienna on 6 December 2019," the EU said in a statement, using the agreement's official name.

"The Joint Commission will be chaired by European External Action Service (EEAS) Secretary General Helga-Maria Schmid and will be attended by the E3+2 (China, France, Germany, Russia, United Kingdom) and Iran."

European efforts to shield Iran from the effects of US sanctions by creating a mechanism to carry on legitimate trade with the Islamic republic have borne little fruit, much to Tehran's frustration.

The EU is growing increasingly concerned by Tehran rowing back from its commitments, notably by stepping up uranium enrichment, and earlier this month Germany warned that the dispute resolution mechanism in the deal could be triggered if Iran continued down this path.

This mechanism has numerous stages with numerous deadlines, but after a process probably lasting several months, it can eventually culminate in the UN Security Council voting on whether Iran should still have relief from sanctions lifted under the deal.