Inspectors from the UN nuclear agency have arrived in Tehran to visit a nuclear facility that has long been off-limits to outside experts.

As the Associated Press reported citing the semi-official Mehr news agency, two inspectors from the International Atomic Energy Agency will visit the heavy water production plant in the central city of Arak tomorrow (December 8). It did not give any further details.

Iran agreed last month with the IAEA to allow expanded UN monitoring at the country's nuclear sites, including the Arak facility.

That agreement was not part of a separate interim deal which Iran also struck last month with world powers. The six-power deal commits Tehran to freeze its nuclear programme for six months in return for limited relief from economic sanctions.