Police in Vietnam have launched a criminal investigation into the illegal burial of a huge amount of waste dump, with Formosa Ha Tinh Steel among the parties to be inspected, local media reports.

The Vietnamese unit of Taiwanese steel company, Formosa Plastics Group, is already under fire for April’s mass fish deaths in the southeast Asian country.

According to state-run media Tuoi Tre, the firm is suspected of illegally sending almost 391 tonnes of cyanide-laced mud to a local company for burial at multiple locations near the plant in Vietnam’s north-central province of Ha Tinh.

“The cyanide content exceeds the hazard level, so we decided to begin a probe into this case,” Bui Dinh Quang, deputy director of the Ha Tinh police department, told Tuoi Tre.

The waste was discovered on July 11 after a worker was caught using an excavator to bury waste at a farm.

Formosa acknowledged in June that it was responsible for what Vietnamese officials say was the country’s worst environmental disaster. The firm has pledged to pay $US500 million in compensation.

– with other agencies