The negotiations will be separate from broader talks in Vienna between Iran and major powers that are mediated by the EU, the bloc's top diplomat Joseph Borrell said Saturday in Tehran.

Iranian foreign ministry spokesman Saeed Khatibzadeh said the talks would focus on the lifting of sanctions imposed by Washington on Tehran and be held "in a Persian Gulf country in the coming days, later this week".

The landmark nuclear deal has been hanging by a thread since 2018, when then US president Donald Trump unilaterally withdrew from it and began imposing harsh economic sanctions on America's arch enemy.

US President Joe Biden's administration has sought to return to the agreement, saying it would be the best path ahead with the Islamic republic.

"What we will do in the coming days does not concern the nuclear dimension but existing differences (and) the lifting of sanctions," Khatibzadeh said.

"I hope that we will see positive results emerge from these talks," he told reporters.

"If Washington comes with answers, then we can do the work quickly ... The ball is in Washington's court."

Talks to revive the nuclear deal began in Vienna in April last year but hit a snag in March this year amid differences between Tehran and Washington, notably over a demand by Iran that its Islamic Revolutionary Guard Corps be removed from a US terror list.

During the Vienna talks Iran also repeatedly called for US guarantees that there will be no repeat of Trump's pull-out.

Following talks in Tehran on Saturday, Borrell said that negotiations to revive the nuclear deal would resume within days.

Bilateral US-Iran talks would be held separately in a Gulf country to avoid confusion with the broader Vienna talks, he added.

Neither Borrell nor Khatibzadeh identified the country that would host those discussions.

The 2015 accord known as the Joint Comprehensive Plan of Action was agreed after initial contacts between Iran and the United States in the Gulf sultanate of Oman, which has long maintained good relations with both countries.