US State Department spokesperson Ned Price on Friday called the resumption of negotiations, scheduled for Tuesday in Austria's Vienna, "a healthy step forward".

But Price added that "these remain early days, and we don't anticipate an immediate breakthrough as there will be difficult discussions ahead".

Trump pulled the US out of the Iran nuclear deal in 2018, and President Joe Biden has said rejoining the agreement is a priority for his administration.

The Biden administration and Iran have differed on any conditions for that to happen, including the timing of the lifting of US sanctions against Iran.

The talks will be held to get Iran and the United States over their differences on conditions for returning to the 2015 nuclear deal.

Agreement on the start of discussions came after talks on Thursday brokered by other governments that have remained in the accord, known as the Joint Comprehensive Plan of Action.

Price said next week's talks will be structured around working groups that the European Union was forming with the remaining participants in the accord, including Iran.

"The primary issues that will be discussed are 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," Price said.

The US, like Iran, said it did not anticipate direct talks between the the two nations now. Price said the US remains open to that idea, however.

Iranian Foreign Minister Mohammad Javad Zarif immediately stressed that no meeting was planned between officials from Iran and the U.S.

In a tweet, Zarif said the aim of the Vienna session would be to "rapidly finalise sanction-lifting & nuclear measures for choreographed removal of all sanctions, followed by Iran ceasing remedial measures".

Any return of the US would involve complications.

Iran has been steadily violating the restrictions of the deal, like the amount of enriched uranium it can stockpile and the purity to which it can enrich it.

Tehran's moves have been calculated to put pressure on the other nations in the deal - Russia, China, France, Germany and Britain - to do more to offset crippling sanctions reimposed under Trump.

Iran has said that before it resumes compliance with the deal, the US needs to return to its own obligations under the deal by dropping the sanctions.

The International Atomic Energy Agency has said that over the past two years, Iran has accumulated a lot of nuclear material and new capacities and used the time for "honing their skills in these areas".

The ultimate goal of the deal is to prevent Iran from developing a nuclear bomb, something the country insists it doesn't want to do. Iran now has enough enriched uranium to make a bomb, but nowhere near the amount it had before the nuclear deal was signed.

Australian Associated Press