The US Department of Justice has become involved in the saga surrounding Hewlett-Packard spying on its own directors and journalists covering the company.

HP acknowledged in a Securities and Exchange Commission filing that it is co-operating with an inquiry into whether tactics used by investigators hired by HP to investigate news leaks from the company's board members had broken the law. HP described the inquiry as "informal" and said the questions are similar to those asked by the attorney general of California.

A spokesman for the US Attorney's Office in San Francisco, said the FBI is joining the US Attorney in "investigating the processes employed" by HP.

The probes are looking into the use of "pretexting" to search phone records to determine which board members may have been talking to reporters. The phone records of nine reporters from several organisations were also obtained to determine who their sources from within HP might have been on stories about the company.

California Attorney General Bill Lockyer says a crime was committed in connection with the pretexting, but his office is still investigating what crime and by whom. Yesterday, the two top ranking members of the US House Energy and Commerce Committee asked HP chairman Patricia Dunn to disclose the identities of the outside firms that conducted the investigation for the board.

An HP spokesman said the company "intends to co-operate ... and will provide the necessary facts and information requested by the subcommittee." HP has previously declined to identify the private firms employed to conduct the probe.

The scandal has brought pressure on Dunn, who ordered the investigation but claims that she didn't know the outside investigative firm hired to trace the leaks would use pretexting. HP's board met yesterday for the second straight day to discuss its response to the controversy but has yet to make a formal announcement over its deliberations.

Former HP director Thomas Perkins, who quit in protest in May because of the way the investigation was conducted, called on Dunn to resign. His statement was in turn prompted by Dunn's comments in interviews last week in which she alleged that it was Perkins who wanted "more aggressive measures" used to investigate the leaks, including use of lie detectors on board members.

The Federal Communications Commission is also investigating HP. The FCC reportedly sent a "letter of inquiry" to AT&T asking how its customer phone records may have been accessed.

HP's internal probe identified director George Keyworth as the source for a CNet story in January about HP's strategy. He refused to resign when asked to do so by Dunn in May, but the board has since voted not to renominate him to his seat.