The U.S. government is investigating the very serious allegations from Google Inc. that hackers, probably from China, sought to access the Gmail accounts of senior U.S. officials, Secretary of State Hillary Clinton said on Thursday.

We are obviously very concerned about Google's announcement regarding a campaign that the company believes originated in China to collect the passwords of Google email account holders, Clinton told reporters, Reuters reported.

Clinton referred further questions to the FBI, which will be conducting the U.S. investigation. On Wednesday, Google said the targeted accounts included those of senior U.S. government officials, as well as Chinese activists and journalists.

This campaign, which appears to originate from Jinan, China, affected what seem to be the personal Gmail accounts of hundreds of users, Google said in a blog posting by Eric Grosse, the Engineering Director of Google's Security Team.

The Chinese government responded angrily, claiming no involvement whatsoever.

Allegations that the Chinese government supports hacking activities are completely unfounded and made with ulterior motives, said Chinese Foreign Ministry spokesman Hong Lei.

Clinton said the U.S. believed cyber issues would be a continuing problem; and that the United States has recently appointed its first ever 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, Clinton said.