U.S. Secretary of State Hillary Clinton says federal agents are investigating accusations from Internet giant Google that computer hackers in China broke into the e-mail accounts of hundreds of people, including senior U.S. officials, Chinese political activists and journalists.

Clinton, speaking Thursday in Washington, called the allegations “very serious,” but offered no details of the probe. She said the FBI is working with Google to investigate the attacks.

Google says the effort to steal user passwords from Google e-mail accounts originated in Jinan in eastern China. It gave no details of whose accounts were violated. The White House said earlier it had no immediate reason to believe that any U.S. government accounts were attacked. The company did not specify which U.S. officials were affected, or how long the users' accounts were exposed.

At a foreign ministry briefing Thursday, Chinese spokesman Hong Lei said it is “unacceptable” to blame China for the attack. The spokesman also referred to a dispute last year that led to a lengthy delay in the renewal of Google's license to operate in the country.

Google says the hackers gained the information with a scam called phishing. Victims are lured into revealing passwords and other information by responding to fake messages that appear to have come from friends or other trusted sources.

Google complained of a much wider cyber attack by Chinese-based hackers last year, which led it to move its popular Chinese search engine to Hong Kong out of the reach of Chinese Internet censors.

Beijing tightly controls Internet material to shield users from what it says is harmful material such as pornography. But human rights groups accuse China of censoring critics of the Communist-run government, and blocking sites that carry what it considers subversive material. Many Western news organizations, including VOA, often see their Web sites blocked in China. This year, sites reporting on the popular uprising in the Middle East have been blocked.