Google received a so-called "second request" from the DOJ asking for more details with which to evaluate the deal. The acquisition is Google's largest ever and would marry the top search company with one of the biggest sellers of Android-based devices.

"While this means we won't be closing right away, we're confident that the DOJ will conclude that the rapidly growing mobile ecosystem will remain highly competitive after this deal closes," Google said in a on its Public Policy Blog. It called the request "pretty routine."

Its dominance of the search market means Google is no stranger to regulatory scrutiny. Its acquisitions of AdMob and ITA Software, among others, were examined closely, and the Justice Department also reviewed its settlement with publishers over Google Books.

Google said last month it would , a move that will and give it control over the development of some Android-based devices.