Federal regulators have begun a formal antitrust investigation into Google's business practices.

In a blog post Friday, the Internet search giant said it received notification from the Federal Trade Commission of the review on Thursday.

Google said "it's still unclear exactly what the FTC's concerns are."

But the inquiry is expected to focus in large part on whether Google abuses its dominance of Internet search to extend its influence into other lucrative online markets, such as mapping, comparison shopping and travel. Rivals complain that Google, which handles two out of every three Internet searches in the U.S., manipulates its results to steer users to its own sites and services and bury links to competitors.