San Francisco: The US Federal Trade Commission is expanding its antitrust probe of Google, the world's most popular search engine, to include scrutiny of its new Google+ social networking service, according to two people familiar with the situation.

The competition issues raised by Google+ go to the heart of the FTC's investigation into whether the company is giving preference to its own services in search results and whether that practice violates antitrust laws, said the people, who declined to be identified because the probe isn't public.

Google last week introduced changes to its search engine so that results feature photos, news and comments from Google+, naming the new function ‘Search, Plus Your World.'

Users who opt for Google+ see personal information about their friends included from the social networking service when they enter a query. The changes sparked a backlash from bloggers, privacy groups and competitors who said the inclusion of Google+ results unfairly promotes the company's products over other information on the web.

Cecelia Prewett, an FTC spokeswoman, declined to comment on the widening of the agency's investigation. Google disclosed the probe on June 24.

‘Benefit consumers'

"We believe that our improvements to search will benefit consumers," Adam Kovacevich, a spokesman for California-based Google, said in an email. "The laws are designed to help consumers benefit from innovation, not to help competitors."

He declined to comment on the FTC investigation.

The Electronic Privacy Information Centre urged the FTC to investigate Google for the search changes, according to a January 12 letter posted on its site. In the letter, the group raised concerns about the company's ‘business practices'.