U.N. nuclear inspectors are in Iran on a long stalled visit meant to investigate suspicions that Tehran worked on nuclear weapons, a charge the Islamic Republic denies.

The official IRNA news agency is quoting Iranian nuclear spokesman Behrouz Kamalvandi as saying that inspectors from the Vienna-based International Atomic Energy Agency arrived in Tehran on Wednesday to discuss "unresolved issues" surrounding a military site in Marivan, in western Iran.

A 2011 IAEA report indicated that large-scale high-explosive experiments were conducted in Marivan, near the Iraqi border.

Talks with the IAEA are parallel to Iran's nuclear negotiations with world powers seeking a permanent agreement on curbing the country's nuclear activities by June 30 in return for the lifting of economic sanctions.

Iran insists its nuclear program is for peaceful purposes only.