Ukraine's state nuclear power company says Russian troops occupying the Zaporizhzhia nuclear power plant in the country's south have been doing unauthorized construction work.

Energoatom issued a statement on Tuesday. It said the Russians have been secretly "carrying out unauthorized construction works on the territory of the Dry Spent Nuclear Fuel Storage Facility" at the plant.

It also said Ukrainian personnel and representatives of the International Atomic Energy Agency at the plant are not allowed to enter the construction site.

The firm mentioned Russia's unverified claim that Ukraine may use a "dirty bomb" -- a conventional explosive that scatters radioactive material.

Energoatom said it "assumes that such actions of the invaders may indicate that they are preparing a terrorist act using nuclear materials and radioactive waste stored at" the plant.

The firm called on the IAEA to make an assessment of the Russians' actions as soon as possible.

Meanwhile, IAEA Director General Rafael Grossi said in a statement on Monday that the UN nuclear watchdog is preparing to send teams of inspectors to two nuclear locations in Ukraine, at Kyiv's request.

The IAEA has not disclosed which Ukrainian facilities it will inspect. But it said it is preparing to visit them in the coming days.

Grossi said the locations are under IAEA safeguards and have been visited regularly by its inspectors.

The director general added that the agency inspected one of the locations one month ago. He said, "No undeclared nuclear activities or material were found there."

Ukraine's Foreign Minister Dmytro Kuleba said on Tuesday that Kyiv invited the agency to send a mission to visit facilities in his country to refute Russia's allegations about a dirty bomb.