FRANKFURT/TOKYO, Sept 8 (Reuters) - Auto supplier Bosch ROBG.UL said it had approached antitrust authorities in Brazil after an internal investigation revealed it had been operating a cartel in spark plugs together with Japan's NGK Spark Plug Co 5334.T .

"We have reported ourselves to the authorities," a spokesman for Bosch said on Monday. Bosch said it could not reveal further details given the ongoing nature of the investigations.

NGK was not immediately available for comment.

German daily Handelsblatt had reported that Bosch had contacted regulators about its activities in Brazil.

Last month the U.S. Department of Justice said NGK Spark Plug had agreed to plead guilty and pay a $52.1 million criminal fine over its role in fixing prices and rigging bids for contracts to supply spark plugs and other automotive parts. ID:nL2N0QP1T5

(Reporting by Edward Taylor in Frankfurt and Maki Shiraki in Tokyo; Editing by David Holmes) ((Edward.Taylor@thomsonreuters.com; +49 69 7565 1187; Reuters Messaging: edward.taylor.thomsonreuters.com@reuters.net))

Keywords: ROBERT BOSH NGK SPARK PLUG/BRAZIL