Iran nuclear deal talks will resume in Vienna on Tuesday, diplomats said Monday, after negotiators in recent weeks have cited progress in seeking to revive the 2015 landmark accord.

Parties to the deal have been negotiating in Vienna since last year with indirect US participation. Talks were most recently halted at the end of last month, and the negotiators returned to their capitals for consultations.

"The 8th round of the Vienna Talks... attended by China, France, Germany, Russia, United Kingdom, Iran and the United States resume tomorrow in Vienna," tweeted Alain Matton, spokesman of the EU, which chairs the discussions.

After months of stalemate, progress has been made in recent weeks to revive the 2015 agreement that was supposed to prevent Iran from acquiring an atomic bomb, a goal it has always denied pursuing.

Former US president Donald Trump unilaterally withdrew from the pact in 2018 and reimposed tough economic sanctions on Iran, prompting the Islamic republic to begin pulling back from its commitments under the deal and step up its nuclear activities.

'Decisive moment' 

German Chancellor Olaf Scholz told the Washington Post in an interview published online on Monday that a successful conclusion of the talks "depends on Iran".

"We gave them a clear message that now this is the time for decisions and for progress, and not for prolonging the process," he was quoted as saying.

"This is the decisive moment, and we hope that they will use the chance. We have not too much time left."

Iranian Foreign Ministry spokesman Saeed Khatibzadeh said the answers "the United States brings tomorrow to Vienna will determine when we can reach an agreement". 

"We have made significant progress in various areas of the Vienna negotiations" including on guarantees that Iran seeks that a new US administration would not breach the deal once again, Khatibzadeh told reporters.

"We hope that what are deemed positive statements will turn into commitments in action and we will be able to reach a good and reliable agreement in Vienna," Khatibzadeh said.

Iran's top security official, Supreme National Security Council secretary Ali Shamkhani, said Sunday that Washington and Tehran had so far failed to produce "balance" in their commitments during the Vienna talks.

The US State Department on Friday said it was waiving sanctions on Iran's civil nuclear programme in a technical step necessary to return to the JCPOA.

The waiver allows other countries and companies to participate in Iran's civil nuclear programme without triggering US sanctions on them, in the name of promoting safety and non-proliferation.