U.S. antitrust regulators told Google they opened a formal investigation into whether the dominant search company illegally abuses its market power. "Yesterday (Thursday), we received formal notification from the U.S. Federal Trade Commission that it has begun a review of our business, Google wrote in its official blog. "We respect the FTC?s process and will be working with them (as we have with other agencies) over the coming months to answer questions about Google and our services."

Google defended its practices, saying it focused on the consumer. "It's still unclear exactly what the FTC's concerns are, but we're clear about where we stand," Google said in the blog.

Google also highlighted its efforts to provide answers to users through Google search, to label advertisements clearly in ordrer users to distinguish advertisements from organic search results and to remain transparent by offering information to webmasters diagnostic tools, support forum, and YouTube.

"These are the principles that guide us, and we know they?ll stand up to scrutiny. We?re committed to giving you choices, ensuring that businesses can grow and create jobs, and, ultimately, fostering an Internet that benefits us all," Google added.

Google has been accused by competitors of favoring its own services over rivals in its search results.

U.S. antitrust regulators have been concerned about Google's dominance of the Web search industry. Google has been also under investigation by the European Commission since last November.