In a statement, the EU and the foreign ministers of France, Germany and Britain -- the three EU powers that led the initial nuclear negotiations with Iran -- said they took note "with regret and concern of the decision by the United States not to extend waivers with regards to trade in oil with Iran".

They also said they were concerned by the US decision "not to fully renew waivers for nuclear non-proliferation projects in the framework of the JCPoA (Joint Comprehensive Plan of Action)" -- the title of the nuclear deal.

Washington on Friday unveiled additional sanctions on Iran's export of enriched uranium as specified under the 2015 deal, although it said it would still grant waivers to permit the deal to continue.

US President Donald Trump last year withdrew his country from the Iran deal, which still has the support of the UN Security Council and the remaining signatories to the accord: Russia, China, France, Britain, Germany and Iran.

The objective of the deal was to prevent Iran working to develop nuclear weapons technology. Tehran agreed to the nuclear restrictions in return for a lifting of sanctions originally imposed by Trump's predecessor, Barack Obama.

Nuclear inspectors have certified that Iran has stuck by the terms of the deal.

But Trump, surrounded by hawkish aides, has been progressively ratcheting up sanctions pressure on Iran, demanding it also rein in its conventional military missile programme and pull its forces and proxy fighters out of other Middle East countries.