The world's largest search engine says it has discovered a major hacking attack that targeted its e-mail accounts over the past year.

Google says several hundred of its Google Mail or Gmail accounts, including those of top South Korean and U.S. officials, have been hacked. The search engine says the attack has been traced to China's Shandong province but added it could not definitely state its exact origins.

The U.S. government says it received the information from Google and that it considers the allegation very serious. The White House says President Barack Obama has been briefed and related agencies led by the Federal Bureau of Investigation (FBI) have begun to investigate.

The Chinese foreign ministry has denied the claim as completely unfounded saying that Google is passing the blame to China.