EU antitrust officials today said they have started an investigation of Microsoft's Windows 2000 amid complaints that the new operating system will give the company a dominant position in the software market.

Mario Monti, the EU competition commissioner, said several customers and competitors have expressed concern at the antitrust implications of Windows 2000, designed for high-powered computers and networks for business. It is the successor for NT.

"Whoever gains dominance in the software service market gains dominance in electronic commerce too," Mr Monti said, adding that the EU sent Microsoft a letter last week, asking for more information. Microsoft has four weeks to respond to the request.

"Microsoft has designed (Windows 2000) in a way which may permit it to leverage its dominant position in PC operating systems into operating markets such as server operating systems and e-commerce," Mr Monti said.

The EU action means Microsoft could face a two-pronged legal attack. In the US, the justice department is weighing up its options with the software giant after a judge rule that Microsoft is a monopoly. But Mr Monti noted that it would be "hugely premature" to talk about possible sanctions against Microsoft.

Microsoft said it looked forward to providing information requested by the EU. "We received the request for information. They have asked us to provide the information by the beginning of March and we look forward to doing that," said John Frank, Microsoft's European director of law and corporate affairs."

Mr Frank said the commission's action followed a complaint filed last year by Sun Microsystems, which he said had complained that advances on Windows 2000 would make it harder for Sun to compete. "We have shared a great deal of information with Sun. We strongly support high quality interoperability," Mr Frank said.