Talks between Iranian nuclear officials and the IAEA team, the first such discussions in more than three years, will last for three days in Tehran, Britain's The Guardian newspaper reported.
Iran has long denied its nuclear program is seeking to make nuclear weapons, contending its research is purely for scientific and civil uses.
The IAEA team, led by the agency's chief inspector, Herman Nackaerts, and assistant director general, Rafael Grossi, said it is seeking explanations for evidence that supports the idea the country has experimented with nuclear weapons design.
"We are not saying that Iran has one, two or three nuclear devices. We are saying that Iran has, at different stages of development, technology that is directly linked to the development of a nuclear device," Grossi said. "The important thing is that Iran gives unfettered access to people, sites and information. The first step is to agree on the process. We will probably not see an outcome for some months to come."
Earlier this month, Grossi said that should Iran refuse to discuss the suspected weapons work, the IAEA would "call the board of governors, who will take the issue to the Security Council."
"It would be very serious for Iran as, up until now, China and Russia have blocked sanctions on the grounds that Tehran is cooperating with the agency. If the IAEA tells the world that Iran is not cooperating, Russia and China will be left without justification for their support," he said.