Japan's health ministry says it will launch an investigation into a report that a subcontractor at the Fukushima nuclear plant instructed workers to take measures to tamper with radiation-detection devices meant to ensure their safety.

The Asahi Shimbun newspaper reported in its Saturday edition that an executive at the construction company Build-Up had told its workers to cover their dosimeters with lead casings while working in areas of Fukushima known to have high radiation levels.

The measure appears to have been meant to keep down the level of radiation measured by the devices to allow the workers to continue working for an extended period of time. The report cited an audio recording one of the workers had made of a meeting with the Build-Up executive alleged to have given the order.

"Unless we hide it with lead, exposure will max out and we cannot work," the executive reportedly said in the recording.

The newspaper said some of the workers quit after refusing to comply with the demand.

Those who stayed spent about four months working at Fukushima, according to the Kyodo News agency.

An earthquake measuring 9.0 on the Richter scale hit northern Japan on March 11, 2011, triggering a tsunami that seriously damaged cooling equipment at the Fukushima nuclear facility. This led to reactor meltdowns, with high levels of radioactivity leaking from the plant, forcing tens of thousands of local residents to flee. More than a year later large areas around the plant remain off limits to the public due to unsafe levels of radiation.

The Fukushima disaster also had an impact on German politics, as it led Chancellor Angela Merkel's center-right government to pass legislation that will see the country shut down all of its nuclear power plants by 2022.

pfd/tj (AFP, Reuters)