"These remain early days, and we don't anticipate an immediate breakthrough as there will be difficult discussions ahead. But we believe this is a healthy step forward," State Department spokesman Ned Price said.

"We do not anticipate presently that there will be direct talks between the United States and Iran through this process, though the United States remains open to them," he said.

The European Union announced Friday an in-person meeting in Vienna of all parties to the 2015 nuclear deal, formally known as the Joint Comprehensive Plan of Action, from which former president Donald Trump withdrew.

The Europeans said it would have "separate" contacts in Vienna with the United States and Iran quickly rejected a direct meeting with its arch-enemy as it presses President Joe Biden first to lift sanctions.

Price said that the "primary issues" for discussion in Vienna will be "the nuclear steps that Iran would need to take in order to return to compliance with the terms of the JCPOA, and the sanctions relief steps that the United States would need to take in order to return to compliance as well."

Iran has insisted that the United States must act first on removing the Trump sanctions, which include a unilateral effort to stop all its oil exports, before it will roll back measures away from compliance that it had taken as a protest.

The Vienna talks will also include the governments of Britain, China, France, Germany and Russia which all remain parties and supporters of the nuclear deal negotiated under former US president Barack Obama.