Iran and international nuclear inspectors failed to reach agreement on starting a probe into Iran’s alleged nuclear weapons programme, a senior International Atomic Energy Agency (IAEA) official said on Wednesday after talks between the two sides.

“We must recognize that our best efforts have not been successful so far,” IAEA chief nuclear inspector Herman Nackaerts said in Vienna after the tenth round of negotiations since early 2012.

Iran’s IAEA envoy Ali Asghar Soltanieh said the discussions on an agreement that would allow access to Iranian nuclear sites, documents and officials were “constructive and intensive.” He added that “the aim of all these elaborations is to bridge the gap towards the conclusion of the text by the next meeting.” Mr. Nackaerts and Mr. Soltanieh said they wanted talks to continue, but no date for a new round was agreed.

While Iranian nuclear officials talked in Vienna, Tehran’s chief nuclear negotiator Saeid Jalili was in Istanbul to meet EU foreign policy chief Catherine Ashton to prepare the ground for the next full round of talks with the permanent UN Security Council members China, Britain, France, Russia and the United States, plus Germany.

Iran would not change its nuclear stance after the June presidential election, Mr. Jalili warned the so—called P5+1 group ahead of his evening meeting with Ashton.

The nuclear programme is a national matter and, therefore, stands above party politics, Mr. Jalili said, stressing that his country has the right to use civilian nuclear technology.

The group of six has been trying to pressure Tehran to stop enriching uranium, fearing that this know-how might be used to make nuclear weapons fuel. Iran says it is making reactor fuel, not nuclear arms.

US Undersecretary for Political Affairs Wendy Sherman said at the Senate on Wednesday that the P5+1 were still waiting for signs that Tehran would seriously address a new offer of easing of some sanctions in return for an enrichment stop, which was presented at talks in Almaty in February.

“We are not interested in talks for talks’ sake, but we must give diplomacy every chance to succeed,” she told the Senate’s Foreign Relations Committee.

Neither the IAEA nor the six—country group have made progress in negotiations with Iran this or last year. Diplomats had said they had not expected progress this week.

They also noted that Mr. Jalili is a presidential candidate and was unlikely to continue in his current role after the June 14 election.

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