"While the UK remains fully committed to the deal, Iran must immediately stop and reverse all activities inconsistent with its obligations," the British Foreign Office said in a statement.

"We are coordinating with other JCPoA participants regarding the next steps under the terms of the deal," it added, referring to the 2015 deal struck between Iran and six world powers including Britain.

Iran made the threat earlier Sunday to breach the pact by starting uranium enrichment above the 3.67 percent limit agreed, unless a solution with signatories can be found in the next two months.

The move comes after the United States quit the deal last year and began to reimpose sanctions against the Islamic Republic, urging European allies to follow suit.

China, France, Germany and Russia are the other parties in the deal.

The European Union has voiced continued support for it but the US measures have severely hampered Iran's vital oil sales and other areas of its economy, stoking renewed tensions.