Google has offered further concessions aimed at ending a three-year investigation into complaints it was blocking competitors and to avert a possible $5 billion fine, the European Commission said on Monday.

The new proposal comes two months after the Commission, which is the European Union's antitrust regulator, asked the world's most popular search engine for more measures to sooth concerns that it was blocking competitors, including Microsoft, in web search results.

"The Commission received a proposal from Google and is assessing it," EU Commission spokesman Jonathan Todd said. He did not provide details nor say if rivals would be given a chance to assess the concessions.

"Our proposal to the European Commission addresses their four areas of concern. We continue to work with the Commission to settle this case," Google spokesman Al Verney said.

Lobbying group FairSearch, whose members include Microsoft and other complainants such as online travel agency Expedia, British price comparison site Foundem and France's Twenga, urged the Commission to seek feedback from rivals.

"Given the failure of Google to make a serious offer last time around, we believe it is necessary that customers and competitors of Google be consulted in a full, second market test," FairSearch lawyer Thomas Vinje said in a statement.

Google, which has a market share of over 80 percent in Europe's Internet search market according to research firm comScore, told the Commission in April it would mark out its services from rival products in internet search results.

It also proposed to provide links to at least three competing search engines and make it easier for advertisers to transfer their search advertising campaigns to rival platforms.

But rivals said Google's offer was inadequate and would only reinforce its dominance.

The Commission has said Google may have favored its own search services over those of rivals and copied travel and restaurant reviews from competing sites without permission.

The EU executive is also concerned the company may have put restrictions on advertisers and advertising to prevent them from moving their online campaigns to competing search engines.