On Monday, the European Union launched two new probes into complaints that Microsoft is using its dominant position to block rival web browsers and office software developers.

The first of the new probes is the consequence of the complaint filed in December by Norwegian-based web browser maker Opera.

According to Oslo-based software developer Opera, which specializes in making the internet available to mobile devices, Microsoft is abusing its market position by selling its Windows operating system together with its Internet Explorer (IE) browser, the complaint said.

"We are filing this complaint on behalf of all consumers who are tired of having a monopolist make choices for them," said at the time Jon von Tetzchner, CEO of Opera.

In a statement issued in December, Microsoft said the computer users already "have complete freedom of choice to use and set as default any browser they wish, including Opera, and PC manufacturers can also pre-install any browser as the default on any Windows machine they sell."

"We will of course cooperate with any inquiries into these issues, but we believe the inclusion of the browser into the operating system benefits consumers, and that consumers and PC manufacturers already are free to choose any browsers they wish," Microsoft added.

The second case announced by the EU on Monday focuses on the claim that Microsoft is refusing to give rivals access to codes that would allow their products to work effectively with Microsoft programmes such as the Office suite, which includes the Microsoft Word text editor and Excel spreadsheet.

That complaint was launched by the European Committee for Interoperable Systems (ECIS), an industry body which includes companies such as IBM, Adobe and Sun Microsystems. Opera is also a member of the European Committee for Interoperable Systems (ECIS), which is known to be a longtime opponent of Microsoft.

The EU investigation will "focus on allegations that a range of products have been unlawfully tied to sales of Microsoft's dominant operating system," the commission's statement said.

The commission stressed that the opening of formal proceedings did not necessarily mean that the complaints were justified.

"The initiation of proceedings does not imply that the commission has proof of an infringement. It only signifies that the commission will further investigate the case," the statement read.

In response Microsoft in a statement said it would "cooperate fully with the Commission's investigation and provide any and all information necessary."

"We are committed to ensuring that Microsoft is in full compliance with European law and our obligations as established by the European Court of First Instance in its September 2007 ruling," Microsoft said.

In 2004, the EU fined Microsoft almost half a billion euros after rivals complained that the US giant had tied its own media player into Windows.

Microsoft challenged that fine in the CFI, but on September 17, 2007 the court ruled in the commission's favour, upholding both the initial fine and a further 280-million-euro penalty for failing to comply with its orders.