"We hope it will be before the end of the Iranian calendar year," Araghchi told reporters in Vienna, referring to March 20.

He said that Iran now had a "clearer picture" of how the new vehicle, known as INSTEX, would work and that its managing director would visit Tehran for discussions "very soon".

But he added that only when the mechanism was fully operational would Iran be able to assess whether it "can work properly and can produce results, (and) can do payments between Iran and European countries".

Araghchi was in the Austrian capital for a "joint commission" with representatives from China, Russia, Britain, Germany and France -- all signatories of the international deal on Iran's nuclear programme.

INSTEX is seen as key to European Union efforts to preserve the deal struck in 2015 between world powers and Iran over its nuclear programme, the Joint Comprehensive Plan of Action (JCPOA).

The US was also a signatory but last May President Donald Trump withdrew from the deal and in November imposed sweeping new sanctions on Iran.

- Remaining members 'united' -

Araghchi said there was "very strong support" for the deal from all participants at the meeting.

He emphasised that Iran expected INSTEX to work "for all goods and commodities, not only humanitarian goods", but that it could start with humanitarian goods "in order to set the patterns for doing business with Iran".

"Once the patterns are set, then other goods, including sanctioned goods -- and oil of course -- would be added to this mechanism," he added.

"It is late but still a move in the right direction," Araghchi said.

INSTEX was launched at the end of January by Britain, France and Germany, who sit on a supervisory board chaired by a UK national. It is registered in Paris.

Russia's ambassador to Vienna's UN organisations, Mikhail Ulyanov, who was also at the meeting, told AFP the remaining signatories to the deal were "united in the need to save the JCPOA".

"There are some problems, particularly in the economic field but we are aimed at overcoming them as soon as possible," Ulyanov said.

He said the speed with which INSTEX became fully operational was up to Germany, France, Britain and Iran.

But Ulyanov added: "I believe it may take a rather long time, at least a few months; most likely even more."

In February the UN's International Atomic Energy Agency watchdog said Iran was adhering to the terms of the JCPOA, under which Tehran drastically scaled back its nuclear programme in return for sanctions relief.

Washington has urged European signatories to the JCPOA to follow Trump's example and withdraw, but this has been rejected by the Europeans.