Japan's Environment Ministry is consulting police about scrap metal that was taken from a dismantled building near the Fukushima Daiichi nuclear power plant before it was tested for radioactivity.
Ministry officials say a subcontractor took the scrap and sold it without permission on multiple occasions since February.
The government had placed an order with a major general contractor to demolish a public library and folklore history building in Okuma Town. Okuma is designated as a "difficult-to-return zone" and an area where decontamination and infrastructure construction are prioritized.
Demolition waste is supposed to be brought to designated sites where it is tested for radioactivity. If the radiation is 100 becquerels or less per kilogram, the debris can be reused in public works and other projects. Otherwise, the waste is to be taken to exclusive intermediate storage facilities or other places.
Ministry officials say they have told the major contractor to ensure that it gives thorough instructions.
Environment Minister Ito Shintaro told reporters on Tuesday that it is extremely regrettable such an incident has taken place. He said the ministry will give strict instructions and supervise the situation so the waste is properly managed.
National Public Safety Commission Chairperson Matsumura Yoshifumi told reporters he's aware that Fukushima police are questioning the subcontractor and taking necessary measures.
He said he believes Fukushima police will respond appropriately based on the law and evidence.
Futaba police, which has jurisdiction over Okuma, told NHK that it has been approached on the issue and is investigating, but will refrain from commenting to avoid hampering the investigation.
Scrap metal prices have been soaring in recent years. An industry organization said demand has been surging from steel makers because of the global trend toward decarbonization.
Prices in the Tohoku region more than doubled in August from four years ago to roughly 330 dollars per ton.