The US State Department is to make a formal protest to China over cyber-attacks on the giant internet search company, Google.
A spokesperson says the United States will demand an explanation.
Google this week threatened to pull out of China because of what it said were hacking attacks and censorship. Beijing has tried to play down the threat.
In response to Google's concerns, China has said that foreign internet firms are welcome to do business there "according to the law".
Google announced late on Tuesday that it was no longer willing to censor its Chinese search engine - google.cn.
Yahoo is also reported to have been targeted by hackers in China, but has not confirmed this.