Google's efforts to fight antitrust allegations against it in Europe appeared to be far from over after regulators rejected the U.S. search company's latest settlement offer.

In an interview aired by Bloomberg TV, the European Union's Competition Commissioner, Joaquin Almunia, said regulators were seeking new concessions from Google following "very, vey negative feedback" from complainants to a proposed settlement announced earlier this year.

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The decision further raised the prospect of EU penalties of up to US$6 billion being imposed on Google over allegations that it abuses its market dominance to undermine competition.

Complainants in the antitrust case accuse the company of manipulating search results to give its own products an unfair advantage over rival Web services.

Explaining the EU's rejection of Google's latest settlement package, Commission spokesman Antoine Colombani said that the complainants had presented new arguments and data that required consideration.

 A Google spokesman said talks with the Commission were continuing to resolve the concerns that the complainants have raised.

The news means that the case, which has been going on for five years, could drag on further.

A Brussels-based antitrust lawyer, Garrigues' Alfonso Madrid, told the Wall Street Journal that some complainants might be stalling the negotiations until a new commissioner assumes office in October.

Foundem CEO Shivaun Raff voiced doubt that Google would be able to come up with an acceptable settlement soon.

"Google's track record in this case makes it clear that it is unlikely to volunteer effective remedies without being formally charged with infringement" of the EU's competition laws," the Wall Street Journal quoted Raff as saying.

Foundem, a U.K. -based comparison search website, was the original complainant in the antitrust case against Google, which controls 80 percent of Europe's Web search market.

Google has linked Foundem to U.S. software developer Microsoft, which has been critical of the Silicon Valley search giant. 

TagsEuropean Union, business regulation, Europe antitrust probes