“The Moscow round of talks has unfortunately not brought any progress in this direction,” Lukashevich said.

However, he said the sides had the political will to resolve the problem.

Western countries led by the United States suspect Iran of pursuing a secret nuclear weapons program, but Tehran insists it needs enriched uranium for peaceful energy generation.

The two-day Moscow talks ended on Tuesday without a breakthrough. The European Union foreign policy chief, Catherine Ashton, who heads the group of mediators, and Russian Deputy Russian Foreign Minister Sergei Ryabkov both said after the talks that there were still “significant differences” between the sides.

The six mediators on Iran’s nuclear issue - Britain, China, France, Germany, Russia and the United States - have been trying to persuade Iran to drop its uranium enrichment program.

Technical experts from both sides have agreed to convene in Istanbul, Turkey, on July 3, to decide whether there are grounds for further high-level negotiations.