Ahead of next month's elections in the Islamic republic, Iran held two sets of talks on Wednesday aimed at easing tensions over its nuclear program in Vienna and Istanbul.
The U.N. atomic agency, the IAEA, in Vienna pressed Iranian officials to grant access to sites, documents and scientists involved in Tehran's alleged efforts to develop atomic weapons.
Separate but linked Wednesday evening talks in Istanbul will see EU foreign policy head Catherine Ashton meet Iran's chief nuclear negotiator Saeed Jalili for the first time since fruitless six-party negotiations in Kazakhstan in April.
The International Atomic Energy Agency says that there is "overall, credible" evidence that until 2003, and possibly since, Iranian scientists conducted research into developing the bomb.
Iran says the IAEA's findings are based on faulty intelligence from foreign spy agencies such as the U.S. CIA and Israel's Mossad -- intelligence it complains it has not even been allowed to see.
Nine rounds of talks since the publication of a major IAEA report in November 2011 have produced no breakthrough.
"As you know differences remain, but we are committed to dialogue and we are determined to solve these issues," IAEA chief inspector Herman Nackaerts told reporters as he went into the talks at Iran's embassy in the Austrian capital, according to AFP.
"We will be working hard today to resolve the differences."
Parallel diplomatic efforts meanwhile between Iran and six major powers -- the U.S., China, Russia, Britain, France and Germany -- are focused more on Iran's current activities, most notably uranium enrichment.
Enriched uranium is at the heart of the international community's concerns since it can be used not only for peaceful purposes such as power generation but also -- when highly purified -- in a nuclear bomb.
The latest round with the "P5+1" in Almaty, Kazakhstan in early April ended with lead negotiator Ashton saying the two sides remained "far apart" despite the P5+1 having sweetened an earlier offer.
According to Reuters, the European Union's top diplomat Catherine Ashton will meet Iran's Jalili - also now a presidential candidate in Istanbul - to discuss a broader diplomatic effort bid to resolve a row that could ignite war in the Middle East.