VIENNA — Iran’s president has promised to back a United Nations probe into suspicions that the country secretly worked on nuclear arms, the U.N.’s chief nuclear inspector said Sunday after talks in Tehran.

Yukiya Amano of the International Atomic Energy Agency described the meetings as “useful.” Still, it was unclear whether his agency would be able to make much progress by Aug. 25 – the deadline agreed on by the two sides to advance an IAEA investigation that has essentially been stalled for seven years.

Amano said Sunday’s talks with President Hasan Rouhani resulted in Iran’s “firm commitment … to resolve all present and past issues” – a euphemism for the IAEA investigation.

But he offered no specifics, and it was clear that stubborn differences remained.

The optimistic note came a day after two diplomats told The Associated Press that the probe was deadlocked.

As part of step by step concessions, Iran agreed in May to cooperate with agency suspicions that it experimented with high explosives that can be used to set off a nuclear charge, and that it modeled a nuclear warhead from uranium metal.

But the diplomats – who are familiar with the investigation but demanded anonymity because they are not authorized to discuss it – said that since then, Iranian officials had ignored repeated IAEA requests for information.

Amano’s trip was meant to kick-start the stalled probe, they said.

Iran’s official IRNA news agency cited the country’s nuclear agency chief, Ali Akbar Salehi, as urging Amano to close the books on allegations that Iran also tested detonators as part of nuclear weapons experiments. But Amano said in a statement that his agency was not yet ready to do so, even while acknowledging that such detonators could be used in the oil industry, as Tehran claims.

Iran insists it has never worked on nuclear arms, describing such allegations as based on false intelligence from Israel, as well as the U.S. and its Western allies.

It also asserts that its present nuclear programs are purely for peaceful purposes. Still, it is negotiating with the U.S. and five other world powers on reducing uranium enrichment and other activities that could be turned from making nuclear fuel toward creating the core of an atomic missile. It hopes in return for an end to nuclear-related sanctions crippling its economy.

The IAEA investigation is separate from those talks. But Washington has said that any overarching nuclear agreement that lifts Iran sanctions must include assurances from the agency that it was able to complete its probe to its satisfaction.

The U.S. also seeks to curb Iran’s long-range missile program as part of the negotiations. That’s something Iran rejects, and IRNA on Sunday cited Rouhani as repeating his country’s objections.

Iran’s long-range missile program is of major concern to Israel, which fears it may one day mount nuclear warheads on the projectiles and has not ruled out military action to prevent that from happening. Iran insists the missile program is a vital deterrent to a possible Israeli attack.

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