"After the talks in Tehran, Bagheri will go to Brussels to discuss outstanding issues," foreign ministry spokesman Saeed Khatibzadeh told reporters, referencing talks last week in Tehran with EU envoy Enrique Mora.

Khatibzadeh only spoke of talks with the EU, rather than the direct parties to the 2015 deal, suggesting that a lawmaker on Sunday misquoted Foreign Minister Hossein Amir-Abdollahian in citing him as saying that the Brussels talks would be with the "P4+1".

The "P4+1" represent four UN Security Council permanent members -- Britain, China, France and Russia -- along with Germany.

These nations are the remaining parties to the 2015 deal with Iran, after the US pulled out in 2018 under then president Donald Trump.

The deal, which gave Iran sanctions relief in return for curbs on its nuclear activities, has been on life support since the US withdrawal, which was followed by Washington reimposing biting sanctions on Tehran, which has incrementally rolled back its commitments.

Talks got underway in Vienna in April in a bid to revive the deal, after Trump's successor President Joe Biden signalled a willingness to come back on board. But they have been suspended since June, when ultraconservative Ebrahim Raisi was elected president of Iran.

Iran has repeatedly said in recent weeks that it is seeking to return to full talks soon in Vienna with the P4+1, but has set no date for doing so, amid growing impatience from the other side.

The US has only participated indirectly in the Vienna talks, as the P4+1 seek both to bring Washington back into the agreement and persuade Iran to return to its nuclear commitments.

Tehran demands that Washington terminate sanctions ahead of any return to its own commitments.

Khatibzadeh said Monday that "obstacles and challenges behind the lack of progress in six rounds of talks in Vienna must be discussed" with the EU in Brussels.