The head of the International Atomic Energy Agency says it has begun inspections at two nuclear locations in Ukraine that Russia alleges is involved in the production of a "dirty bomb" designed to disperse radioactive material.

IAEA Director General Rafael Mariano Grossi issued a statement on Monday saying agency inspectors had begun verification activities at the two sites at Ukraine's request.

He said the inspection "would soon complete" and his initial conclusions would be released later this week.

IAEA inspectors have been visiting the two locations regularly. The agency said it inspected one a month ago and found no undeclared nuclear activities or materials.