LONDON — Days after Iran struck a landmark accord with world powers on its nuclear program, the International Atomic Energy Agency announced on Thursday that Tehran had invited its inspectors to visit a heavy-water production plant linked to the deal — the first tangible step since the agreement was concluded.

In a speech in Vienna, the agency’s director general, Yukiya Amano, said the invitation was for inspectors to travel to the plant in Arak, in central Iran, on Dec. 8. Mr. Amano told reporters that it was “for sure” that inspectors would accept the offer.

The invitation was limited to the heavy-water production facility on the same site as a reactor that is under construction and to which international inspectors have had some access, Mr. Amano said. The facility producing heavy water, used in some types of reactors to control nuclear activity, has been off limits to inspectors for more than two years.

Part of the deal reached with world powers in Geneva specifically provided for Iran not to produce fuel for the Arak plant, install additional reactor components there or put the plant into operation. If it became fully operational, the reactor would produce plutonium that could be used in a nuclear weapon.