The US government broadened its legal attack on Microsoft yesterday by accusing the world's largest software company of trying to intimidate sector giants to protect its monopoly position.

In court filings published yesterday, the justice department and 20 state attorneys-general shifted their case away from the battle over the marketing of internet software and towards Microsoft's monopoly position in the wider computer industry.

The government said the company had sought to stop Intel, the world's largest microprocessor producer, from developing its own software. It also said Microsoft further attempted to stop Apple, its bitter rival in operating systems, from marketing internet video software in competition with its own.

Microsoft's attempts to win agreements with rivals was "part of a pattern of using its control over the monopoly operating system to make competing products operate, or appear to operate, less effectively", the government said.

The government's arguments mark a turning point in nine years of antitrust investigation of Microsoft and litigation, initially by the Federal Trade Commission and then by the justice department.

In its initial lawsuit, filed in May, the government accused the company of attempting to stifle Netscape Communications, Microsoft's internet software rival.

The government has hesitated to broaden its case, partly because of the difficulty of devising remedies that would prevent continued alleged abuses. A break-up of the company, for example, could have substantial negative effects throughout the US computer industry.

The government also accused Microsoft executives - particularly Mr Bill Gates, its founder - of "an astonishing lack of recall" in interviews about their actions.

Microsoft dismissed the new allegations as "groundless" and said it was "unfortunate that the government had lost faith in the substance of its case and was now resorting to gratuitous name-calling".