TOKYO, JAPAN:  Japan's Hitachi Ltd and Toshiba Corp said on Tuesday that their optical disc drive operations with South Korean partners were being investigated internationally for possible anti-trust violations.

Hitachi said its joint venture with LG Electronics, Hitachi-LG Data Storage, had received a subpoena from the U.S. Department of Justice, and that the unit was also under investigation by European Union and Singapore regulators.

Toshiba said its joint venture with Samsung Electronics, Toshiba Samsung Storage Technology Corp, had also received a subpoena in the United States and that it was answering queries from authorities in other regions.

Sony the previous day said that its U.S. optical disc drive had received a subpoena in the United States, without elaborating on what products were being investigated.

Optical disc drives read or write data on media such as CDs, DVDs and Blu-ray discs.