(BRUSSELS) - EU competition regulators said Monday they had launched two new antitrust probes against Microsoft, opening fresh fronts in their battle against the US software giant's dominant market power.

The European Commission said one investigation targeted the interoperability of a broad range of software, including Microsoft's popular Office package, with rival products.

The other inquiry would look into whether Microsoft had illegally tied products to its ubiquitous Windows operating system, including its Internet Explorer browser.

"This initiation of proceedings does not imply that the Commission has proof of an infringement," the European Union's top competition watchdog said in a statement.

"It only signifies that the Commission will further investigate the case as a matter of priority."

Microsoft, which has clashed in the past with the Commission over antitrust charges, vowed to help regulators in their latest two investigations.

"We will cooperate fully with the Commission's investigation and provide any and all information necessary," the company said in a statement.

"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," it added.

In September, Microsoft lost an appeal before Europe's second-highest court against a fine of nearly 500 million euros (745 million dollars) that EU regulators slapped on the company in 2004 for abusing its dominant market power.

In that case, the Commission accused Microsoft of using its stranglehold on personal computer operating systems to elbow rivals out of the more competitive markets for media players and operating systems running back-office servers.

The new probes considerably broaden the scope of Microsoft product lines facing regulatory scrutiny while also targeting some of the company's best-known programmes.

Following a complaint from a group of Microsoft's rivals known as ECIS, the Commission said it would look into whether the company had denied competitors key technical information about not only Office, but also servers and other software.

The Commission also said it would follow up a complaint from Internet browser vendor Opera about Microsoft's practice of selling Windows with Internet Explorer included. This could be seen as stifling competition for Internet browsers.

"The Commission's investigation will therefore focus on allegations that a range of products have been unlawfully tied to sales of Microsoft's dominant operating system," it said.

Since its September court defeat, Microsoft has promised to make "substantial changes" in order to comply with regulators' demands.

After the the Commission's announcement, Microsoft shares were showing a gain of 1.35 percent at 34.37 dollars in early trading in New York amid a broadly higher market.

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