The United States withdrew from that landmark deal, which had imposed curbs on Tehran's nuclear development in return for sanctions relief, during US President Donald Trump's first term.

Tehran adhered to the 2015 deal for a year after Washington's withdrawal but then began rolling back its commitments. Efforts to revive the pact have since faltered.

Beijing has said it hopes Friday's talks will "strengthen communication and coordination, to resume dialogue and negotiation at an early time".

A readout of the meeting by Chinese state broadcaster CCTV said the three diplomats "exchanged views on the Iran nuclear issue and other issues of common concern".

State media did not share any further details of the talks, attended by China's Vice Foreign Minister Ma Zhaoxu, Russian Deputy Foreign Minister Sergei Ryabkov and Iranian Deputy Foreign Minister Kazem Gharibabadi.

Trump, who returned to the White House for a second term in January, has reinstated his "maximum pressure" policy of sanctions against Iran, mirroring his approach during his first term.

He has called for new negotiations with Iran, but Tehran has ruled out direct talks while US sanctions remain in place.

This week, Trump sent a letter to Tehran urging nuclear talks -- warning of possible military action if it refuses.

Tehran said Thursday that letter -- which Trump said was addressed to Iran's supreme leader Ayatollah Ali Khamenei -- was currently "being reviewed".

"Ultimately, the United States should lift the sanctions," Foreign Minister Abbas Araghchi said in an interview published Thursday by the government's official newspaper.

"We will enter into direct negotiations when we are on an equal footing, free from pressure and threats, and are confident that the national interests of the people will be guaranteed."

A report dated last month by the International Atomic Energy Agency (IAEA) said Iran had significantly increased its stockpile of highly enriched uranium to 60 percent purity -- close to the 90 percent needed for an atomic bomb.

Iran's supreme leader Khamenei said this week that his country "does not have nuclear weapons" and was "not seeking" them.