The latest round of talks to salvage the Iran nuclear deal have been put on pause, the European Union's coordinator said on Friday, calling for "political decisions" to break the deadlock.

Diplomats have been meeting in the Austrian capital for several weeks straight in the search for a breakthrough to revive the 2015 deal involving Iran, the United States, Britain, China, France, Germany and Russia.

The EU has played the role of mediator and the bloc's Enrique Mora tweeted, "Participants will go back to capital(s) for consultations and instructions to come back next week.

"Political decisions are needed now."

Chief negotiators for Britain, France and Germany put out a statement saying, "Everyone knows we are reaching the final stage, which requires political decisions.

"Negotiators are therefore returning to capitals for consultation."

Russia's representative Mikhail Ulyanov made similar comments on Twitter noting "negotiations have reached advanced stage when political decisions are needed.

"The 8th round is expected to resume next week."

A US State Department spokesperson described January as "the most intensive period of talks on a mutual return to full implementation of the JCPOA to-date", referring to the nuclear deal, known formally as the Joint Comprehensive Plan of Action.

"Everyone knows we are reaching the final stage, which requires political decisions. Negotiators, including (US) Special Envoy (Robert) Malley, are therefore returning to capitals for consultations this weekend."

Talks to rescue the faltering accord began in the Austrian capital in April and, after a five-month suspension, resumed in November.

The deal had given Tehran sanctions relief in exchange for curbs on its nuclear programme.

But after the US pulled out and reimposed sanctions in 2018 under Donald Trump, Iran began dramatically stepping up nuclear activities.

Joe Biden's presidency helped relaunch the negotiations but Washington has been taking part only indirectly, leaving the Europeans to meet the Iranians.

Then on Monday, Iran for the first time said it was open to direct negotiations with the US, which quickly declared itself ready to hold talks "urgently".

"Our understanding is Iran has not yet agreed to direct talks," State Department spokesman Ned Price said Thursday.

"We remain prepared to meet directly," Price told reporters.

France on Friday saw signs the talks could now succeed.

"The negotiations remain difficult as we need to clarify the question of guarantees (on lifting sanctions) and the framework of control over the Iranian nuclear programme," said a French presidential official who asked not to be named.

"Nevertheless there are some indications that the negotiations could succeed," added the official, saying President Emmanuel Macron may hold telephone talks with his Iranian counterpart Ebrahim Raisi in the coming days.

Deal, no deal

Iran also spoke early this week of progress at the talks, adding Washington needed to take political decisions to move forward.

Washington has remained cautious with Brett McGurk, the top White House official on the Middle East, warning Thursday the negotiations could still "collapse very soon".

"We're in the ballpark of a possible deal but, again, I'm not going to put odds on this," McGurk said.

"There's a chance for a deal and there's also a pretty good chance there's not going to be a deal -- and I will tell you we are prepared for either scenario."