BRUSSELS, April 25 - Google's rivals have a month to examine the concessions proposed by the Internet search engine to end an antitrust investigation, EU regulators said on Thursday, in a move that could force the company to improve its offer.

Complainants, which include Microsoft, online mapping services, online travel sites TripAdvisor and Expedia, newspaper publishers and price comparison sites, are likely to demand more concessions.

The world's most popular search engine submitted its proposal early this month after EU regulators outlined four areas of concern about its business practices, saying these could restrict consumer choice and stifle competition.

Google's proposal includes marking out its services from rival products in Internet search results and to provide links to at least three competing search engines.

Specialised websites will be able to opt out from the use of all their content in Google's own specialised search services and will also be able to mark out specific categories of information to prevent its use by Google.

Publishers will be allowed to control the display of their content in Google news and no longer obliged to use online search adverts exclusively from Google.

The search giant will also scrap restrictions preventing advertisers from transferring their search advertising campaigns to rival platforms.

If approved, Google's undertakings would be binding for five years in Europe and monitored by a trustee.