Iran and the world’s six leading powers failed to resolve any point of substance during “tough and frank” negotiations over Tehran’s nuclear ambitions, declining even to fix another meeting.

After two days of talks in Moscow, Baroness Ashton, the European Union’s high representative for foreign affairs, announced that “significant gaps” of “substance” had prevented any progress.

After three such encounters between Iran and the six powers so far this year, there is no guarantee of a fourth, raising the possibility that a diplomatic effort designed to avert the possibility of another war in the Middle East might be drawing to a close.

Lady Ashton, who chairs the “P5 plus 1”, said that both sides had set out their “respective positions” in “tough and frank exchanges,” adding: “It remains clear that there are significant gaps between the substance of the two positions.”

A Western diplomat said: “We don’t want a crisis and a collapse of talks, but it’s very clear there are significant differences over substance and, on that basis, we were not prepared to commit to another round of talks.

“There will be a period of reflection and it’s designed to send a message to the Iranian side that if they want this process to continue, they need to come up with an improved offer that includes concrete steps.”

Critics believe that Iran aims to use the talks to buy time while pressing ahead with its nuclear programme. Anxious to avoid this outcome, western diplomats say they do not want negotiations for the sake of negotiations.

Accordingly, the only agreement in Moscow was to arrange a meeting of experts on July 3 in Istanbul to review the technical aspects of the positions of the two sides. Depending on the outcome of this encounter, senior diplomats from Iran and the “P5 plus 1” – the five permanent members of the UN Security Council (American, Britain, France, Russia and China) and Germany – could meet again, but there is no certainty. Even the question of whether to allow the experts’ meeting to happen was said to have been a difficult one.

The dispute centres on a proposal made by the “P5 plus 1”. They want Iran to stop enriching uranium to 20 per cent purity, ship its existing stockpile of this material out of the country and close a previously secret nuclear plant at Fordow.

Uranium enriched to this level is close to the material required for a nuclear weapon, although Iran says the only intention is to fuel a civilian research reactor.

In return for taking these three steps, the “P5 plus 1” were prepared to ease some sanctions imposed on Iran, notably those restricting the supply of spare parts for civil airliners.

But Saeed Jalili, Iran’s chief negotiator, insisted that the “P5 plus 1” must recognise Iran’s “right” to enrich uranium and lift all sanctions before any steps could be taken. After the talks, Mr Jalili said: “The enrichment of uranium for peaceful purposes for all levels is an inalienable right.”

Six United Nations resolutions, by contrast, urge Iran to stop enriching uranium, a process that could be used to make the core of a nuclear weapon. (© Copyright of Telegraph Media Group Limited 2012. 06/20/12)