TOKYO - Japan's health ministry said it would investigate reports that workers at the stricken Fukushima nuclear power plant were urged by a subcontractor to place lead around radiation detection devices in order to stay under a safety threshold for exposure.

The Asahi Shimbun newspaper reported on Saturday that an executive from Build-Up, a subcontrator to plant owner Tokyo Electric Power, told workers to cover the devices called dosimeters when working in high-radiation areas.

Dosimeters can be worn as badges or carried as devices around the size of a smartphone to detect radiation.

Nine workers wore the lead plates around the devices once after the executive's plea, Public broadcaster NHK said, citing the subcontractor's president.