The move, however, casts doubts on whether European Competition Commissioner Joaquin Almunia will now be able to wrap the case up in the remaining two months of his mandate. He had previously aimed for a decision after the summer break.
Google has to date improved its proposal three times in response to charges from Microsoft, European publishers and competitors across Europe that it was squeezing them out in online search results and blocking advertisers from moving to competing platforms.
Last week rivals stepped up the pressure on Almunia to demand more concessions, saying a proposed deal reached in February was catastrophic for them as it would entrench Google's market share of more than 80 percent in Europe.
In the last two momths 18 companies have responded to Almunia's stated intention to rebuff their grievances.
"In the replies to our letters the complainants have submitted new arguments and data, some of which should be taken in consideration. We are now in contact with Google to see if they are ready to offer solutions," Commission spokesman Antoine Colombani said.
He declined to say whether there was a deadline for Google to respond.
Google spokesman Al Verney said: "We continue to work with the European Commission to resolve the concerns they have raised."
Google's executive chairman, Eric Schmidt, defended the company in a letter in the Financial Times on Saturday, saying there was plenty of competition in the market and that its Internet search service was built for users, not websites.
In an interview with Bloomberg TV on Sept. 6, Almunia said he was reviewing new studies presented by the competitors.
"We are trying to understand the arguments of the complaints and trying to extract from Google solutions to these solid arguments," he was quoted as saying.
"Some of these replies are very very negative, and in some of those replies some complainants have introduced new arguments, new data, new considerations, so we now need to analyse these, and to see if we can find solutions, Google can find solutions."
Lobby group FairSearch, whose members include complainants Microsoft, Finnish telecoms network equipment maker Nokia and online travel site TripAdvisor, expressed doubts as to whether fresh concessions would allay competition concerns.
"The Commission should issue a statement of objections," FairSearch said, referring to a charge sheet and process that could land Google a fine of up to $5 billion.
© Thomson Reuters 2014
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