WASHINGTON (Reuters) - Recent cyber attacks on Google were a "wake-up call" and neither the U.S. government nor the private sector can fully protect the American cyber infrastructure, Dennis Blair, director of national intelligence, said on Tuesday.

"Malicious cyber activity is occurring on an unprecedented scale with extraordinary sophistication," Blair said in prepared testimony for a Senate intelligence committee hearing.

The Chinese military's "aggressive cyber activities" pose challenges to neighbors, Blair said.

(Reporting by Adam Entous, Writing by Tabassum Zakaria; Editing by Doina Chiacu)