A US senator has called for closer scrutiny of Google's business practices in response to claims by rival e-commerce websites they are being treated unfairly.
The probes, led by senator Herb Kohl, chairman of the antitrust subcommittee, come on top of those by the European Commission and Texas attorney general's office.
Critics allege that Google has abused its dominance in online search by unfairly demoting rivals and promoting its own products in search results, according to the San Francisco Chronicle.
These concerns have grown as Google has expanded beyond search into mapping video, restaurant rating and shopping comparison services, the paper said.
Google maintains that its criteria for evaluating sites are based strictly on what best serves users.