Wal-Mart Stores Inc. (WMT) on Tuesday said the U.S. Attorney's Office in Los Angeles has informed the retailer that it is the target of a criminal probe involving the transportation of material deemed "hazardous waste" in allegedly improper vehicles.

In a filing with the U.S. Securities and Exchange Commission, the world's biggest retailer said it is being investigated for violating the Resource Conservation and Recovery Act.

According to the Wal-Mart, the government is investigating whether it improperly used its own trucks to transport material deemed hazardous to centralized facilities, rather than using certified hazardous waste carriers to transport that material directly to designated disposal sites.

The company previously disclosed that it had received a grand jury subpoena in the matter, looking at, among other things, the transportation of material from California to Nevada.

Wal-Mart said in the filing it is cooperating fully with the authorities, but cannot predict any potential loss or range of losses from the probe.