The US Department of Justice has begun a preliminary investigation into the activities of the group of companies developing and promoting the Blu-ray Disc storage format, according to a report in Sunday's online edition of the Wall Street Journal newspaper.

The investigation is into whether the group's members may have acted together to impede the technical progress of a rival standard being developed by the DVD Forum, the newspaper said, citing an unnamed source close to the DVD Forum.

Two of the largest companies backing the Blu-ray Disc format, Matsushita Electric Industrial (Panasonic) and Sony, declined to comment on the report. A Sony spokesman said the company had not seen the report, while a Matsushita spokesman said it was looking into the newspaper story. "This came out of the blue for us," the spokesman said.

The battle between the Blu-ray group and DVD Forum is pitting some of the largest names in consumer electronics and computing against each other, over the format for next-generation optical discs. The discs can store between four and six times as much data as today's DVD discs because they use more advanced blue laser technology, as opposed to red lasers used in DVDs.

A rewritable version of the format has already been standardised and Sony is selling a consumer video recorder based on the format in Japan. The group also recently received the endorsement of Hewlett-Packard Co. (HP) and Dell for a read-only version, which is expected on the market sometime in 2005.

A rival format, called High Definition/High Density DVD (HD-DVD), is currently being developed by NEC and Toshiba under the DVD Forum, which is the standards body that created the DVD format. Many of the Blu-ray Disc backers are also members of the DVD Forum, having played a part in the development of current DVD standards.