The deal -- agreed by Iran, the US, China, Russia, Britain, France and Germany -- offered Tehran sanctions relief in exchange for curbs on its nuclear programme.

But the US unilaterally withdrew in 2018 under then-president Donald Trump and reimposed biting economic sanctions, prompting Tehran to begin rolling back its commitments.

Talks aimed at restoring the deal started last year in Vienna between Iran and countries still part of the accord. The US has been taking part indirectly in negotiations.

"Iran is not currently talking with the US directly", Hossein Amir-Abdollahian said in televised remarks.

"But, if during the negotiation process we get to a point that reaching a good agreement with solid guarantees requires a level of talks with the US, we will not ignore that in our work schedule," he added.

"Our direct talks are with P4+1," he said, referring to Germany and permanent Security Council powers France, China, Britain and Russia.

"And our indirect negotiations with the US currently are... via (EU diplomat Enrique) Mora and one or two other countries present at Vienna talks," he added.

Iran had previously stated that the US must "change course" and return to the nuclear deal, prior to any direct talks between the two arch-foes in Vienna.

"Meanwhile, the US side is sending messages in different ways that it seeks a level of direct talks with Iran," Amir-Abdollahian added during a conference at the foreign ministry in Tehran.

The negotiations, which seek to bring Washington back to the accord and ensure Iran returns to its commitments under the deal, started in April, and resumed in late November, after they were suspended in June as Iran elected ultraconservative President Ebrahim Raisi.

US-Iran relations have been severed since April 1980, just months after the fall of the shah and the occupation of the American embassy by Islamist students loyal to Ayatollah Ruhollah Khomeini.

They worsened significantly after Washington withdrew from the nuclear deal and imposed sanctions on Tehran.

Iran's supreme leader Ayatollah Ali Khamenei, who has the final say on major issues including the nuclear policy, said earlier this month that negotiating with the 'enemy' does not mean surrendering.

"The bullying of the enemy should not be tolerated," he said, referring to the US.

But "negotiating with the enemy some time for example is another thing -- us interacting with them is another thing," Khamenei added in a televised speech.

- Prisoners' release 'possible' -

Some analysts had interpreted these remarks as a tacit signal for possible direct talks with the US, as was the case in the buildup to the 2015 nuclear accord.

Earlier on Monday, Iran's foreign ministry spokesman said it was "possible" to reach an agreement on both the release of Iranian and US prisoners and the nuclear deal.

"They are two different paths, but if the other party (the US) has the determination, there is the possibility that we reach a reliable and lasting agreement in both of them in the shortest time," spokesman Saeed Khatibzadeh told reporters.

Khatibzadeh's comments came in reaction to remarks made by the US envoy for Iran, Robert Malley, who on Sunday said it was unlikely that Washington would strike an agreement unless Tehran releases four US citizens.

The four US citizens held in Iran are Iranian-American businessman Siamak Namazi, 50, and his father Baquer, 85, as well as environmentalist Morad Tahbaz, 66, and businessman Emad Sharqi, 57.

Washington also holds four Iranian nationals.

The two countries have released each others' citizens in the past.