WASHINGTON, Sept 21 (Reuters) - The U.S. Justice Department is conducting a criminal probe after Volkswagen admitted it had rigged emissions tests of diesel-powered vehicles in the United States, Bloomberg reported on Monday, citing two U.S. officials familiar with the inquiry.

The U.S. Environmental Protection Agency said on Friday the world's biggest carmaker by sales used software for diesel VW and Audi branded cars that deceived regulators measuring toxic emissions and could face penalties of up to $18 billion.

Volkswagen said on Sunday it had launched an internal investigation. (Reporting by Sandra Maler; Editing by Eric Beech)

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