Secretary of State Hillary Rodham Clinton said Thursday that Google's allegations of Chinese hacking of its email system are "very serious" and will be investigated by the FBI.
Google said the hundreds of accounts affected by the breach included personal email belonging to senior U.S. officials.
"These allegations are very serious," Clinton told reporters. "We take them seriously. We are looking into them."
She declined to comment further on the matter, referring questions to both Google and "to the FBI which will be conducting the investigation."
Google said Wednesday that personal Gmail accounts of several hundred people, including senior U.S. government officials, military personnel and political activists, had been exposed. Google traced the origin of the attacks to Jinan, China, the home city of a military vocational school whose computers were linked to a more sophisticated assault 17 months ago on Google's systems.
Clinton said attacks such as the one alleged by Google were a prime reason the State Department has for the first time created a cyber-security coordinator. "We know this is going to be a continuing problem and therefore we want to be as prepared as possible to deal with these matters when they do come to our attention," she said.
The Pentagon said Thursday it had very little information since the reported breaches involved personal accounts rather than government email. And since the accounts were not official, the U.S. Department of Defense didn't know whether defense employees were among the targeted individuals, the statement said.
A day after Google exposed the breach, China denied on Thursday that it supports hacking and said it is part of global efforts to combat computer security threats.
Foreign Ministry spokesman Hong Lei told reporters that hacking was a global problem and Chinese networks had also been targeted by hackers, but he gave no specifics. He said China was working to crack down on the problem, but he didn't respond when asked whether it would investigate this specific incident.
"Allegations that the Chinese government supports hacking activities are completely unfounded and made with ulterior motives," Hong said.
Google said all of the hacking victims have been notified and their accounts have been secured.
The hackers appeared to rely on tactics commonly used to fool people into believing they are dealing with someone they know or a company that they trust. Once these "phishing" expeditions get the information needed to break into an email account, the access can be used to send messages that dupe other victims.
China's Ministry of Industry and Information Technology, which has a hand in regulating the Internet, referred questions about the allegations to another regulatory agency, the State Council Information Office, which did not respond to the questions.
The latest attacks aren't believed to be tied to the more sophisticated assault last year. That intrusion targeted Google's own security systems and triggered a high-profile battle with China's Communist government over online censorship.