US computer giant Microsoft today declared war on Internet king Google when it joined officially an anti-trust complaint in Europe that could result in billions of dollars in fines.

It is the first time Microsoft, which was itself hit with eight-figure fines during a decade of Brussels anti-trust action along with US chip-maker Intel, has gone public with submissions to European Union inspectors probing the online search giant.

"Microsoft is filing a formal complaint with the European Commission as part of the Commission's ongoing investigation into whether Google has violated European competition law," read an online posting from Brad Smith, senior vice president and general counsel, Microsoft Corporation.

The move heightens the intensity of the probe against Google launched by EU regulators end November, amid accusations it rigged the search market for consumers.

EU competition watchdogs are investigating whether Google is guilty of "unfavourable treatment" of rival search services providers and whether the company's own services -- including YouTube video, book-scanning or telephony -- are getting "preferential placement" in consumer queries.

The Commission has "taken note" of the complaint and will ask Google for a response, said Amelia Torres, spokeswoman for EU competition commissioner Joaquin Almunia.

Asked to comment, Google said the action was hardly surprising given a Microsoft subsidiary was one of the original complainants in the probe.

"For our part, we continue to discuss the case with the European Commission and we're happy to explain to anyone how our business works," said Google spokesman Al Verney.

The inquiry launched November 30 by the Commission, the European Union's anti-trust regulator, into Google's pre-eminent positioning in search services and online advertising, followed several complaints including one from internet portal Ciao, purchased by Microsoft in 2008.

"We should be among the first to compliment Google for its genuine innovations," said Microsoft's Smith. "But we're concerned by a broadening pattern of conduct aimed at stopping anyone else from creating a competitive alternative."

Google refused to divulge its share of the search services market but the Commission reckons it has clinched a 95 percent stake in Europe.

In the United States, Microsoft says it serves around 25 percent of search needs either directly through Bing or its partnership with Yahoo!.

Citing court action against Google practises in the US, Smith said the situation "is worse in Europe."