Officials from Japan's fair trade watchdog raided the Japanese headquarters of US software giant Microsoft today on suspicion of anti-monopoly law violations.

A official from Japan's fair trade commission, speaking on customary condition of anonymity, said Microsoft Japan was suspected of attaching improper restrictive conditions when signing software deals with Japanese personal computer manufacturers.

These include a requirement that the Japanese companies allow infringement of their patents, the official said, but he refused to elaborate further.

A spokeswoman at Microsoft Japan confirmed that the commission inspected the company's Tokyo headquarters office but denied any wrongdoing.

The company was cooperating with the investigation, which involves questions about the wording on copyright and patents in the licensing agreement with Japanese manufacturers, she said.

A spokesman for NEC Corp, Japan's largest computer maker, also told Reuters that commission representatives had visited its offices to ask questions about its dealings with Microsoft.

Microsoft's Windows operating system software dominates computers sold and made in Japan, as it does in other parts of the world.

The investigation is the latest to involve Microsoft, following accusations that it has abused its monopoly on PC operating systems to push prices higher or harm rivals.

The company is in settlement negotiations with the European commission, which says the firm abused its dominant position and curbed competition by tying its Media Player programme - used for playing music and videos - to its Windows operating system.

Microsoft Japan was investigated by the fair trade commission in 1998, for packaging its internet browsing software Internet Explorer with its operating system and for pushing its word processor and spreadsheet software, Word and Excel, onto its operating system customers.

That investigation was closed without ramifications.