United Nations nuclear experts are in Tehran for meetings they hope will further their investigation into Iran's controversial nuclear program.

The International Atomic Energy Agency team is holding talks with Iranian officials Wednesday. They want to address what they have called “overall, credible” evidence of work by Iran on nuclear weapons research.

The leader of the U.N. team, Herman Nackaerts, said Tuesday the IAEA wants to “finalize a structured approach” for resolving outstanding issues regarding Iran's nuclear program. He also reiterated that U.N. investigators are ready to visit Iran's Parchin military site if the government allows.

Western nations suspect the Parchin facility, southwest of Tehran, is related to possible nuclear weapons development. Iran says it is a conventional military site and that its nuclear program is strictly for peaceful purposes.

Iranian Foreign Ministry spokesman Ramin Mehmanparast said Tuesday that a religious decree issued by Iran's supreme leader banning nuclear weapons is binding on the Iranian government.

The IAEA visit comes as international diplomats are again setting the stage for separate negotiations with Tehran over curbs to its nuclear ambitions.

Iran and the so-called P5+1 contact group – the United States, Britain, Russia, China, France and Germany – are expected to try to open talks in the coming weeks after a seven-month hiatus.

The last time Iran's nuclear negotiators met with their foreign counterparts, in Moscow in June, the talks did not go well. Both sides wanted their maximum demands met, and they offered little in return.