Foreign Minister Mohammad Javad Zarif has expressed Iran's "discontent" to his US counterpart over the expansion of a blacklist of Iranian firms following a landmark nuclear accord, media reported Monday.

Iran has accused Washington of going against the spirit of the deal reached in November by adding a dozen overseas companies and individuals to its blacklist for evading sanctions imposed on Tehran over its controversial nuclear programme.

Under the deal reached in Geneva in November, Iran agreed to freeze some of its nuclear activities in return for some sanctions relief for a six-month period. The agreement is aimed at buying time for a comprehensive accord.

US officials maintain the expansion of the blacklist does not entail additional sanctions, but merely the enforcement of the existing sanctions regime, which helped bring Iran to the negotiating table.

But on Monday the Fars news agency, quoting a foreign ministry statement, said Zarif had "expressed Iran's discontent" during a telephone conversation with US Secretary of State John Kerry, without specifying when the two spoke.

The IRNA state news agency said it was the first conversation between the two top diplomats since the Geneva agreement was reached on November 24.

A State Department official confirmed the telephone call, saying they "discussed the importance of moving forward on implementation of the Joint Plan of Action they agreed to in Geneva and of maintaining a constructive atmosphere as the negotiations continue."

"The conversation was focused on the way forward," the official said, adding that the two spoke during Kerry's overnight Friday to Saturday flight from Israel to Vietnam.

The blacklist decision led to the suspension of technical negotiations in Vienna last week between Iran and the so-called P5+1 -- the United States, Britain, France, Russia and China plus Germany.

But on Sunday, Tehran said the negotiations would continue despite the move.

"We are pursuing the negotiations seriously and of course we will give a well-considered, purposeful, smart and proper reaction to any inappropriate and unconstructive move," Zarif wrote on his Facebook page.

Western nations have long suspected Iran is pursing nuclear weapons alongside its civilian programme, allegations denied by Tehran, which insists its nuclear activities are entirely peaceful.