The United States has asked Beijing to investigate reports that China interfered with Internet content hosted outside the country and used it to attack U.S. websites, the State Department said on Friday.
"We are concerned by reports that China has used a new cyber capability to interfere with the ability of worldwide Internet users to access content hosted outside of China," State Department spokesman Jeff Rathke said.
"The cyber attack manipulated international web traffic intended for one of China's biggest web services companies and turned it into malicious traffic directed at U.S. sites," Rathke told a news briefing.
He said the United States has asked Chinese authorities to investigate the cyber attack and advise Washington of the results.
The Chinese government has repeatedly denied it has anything to do with hacking.
China's "Great Cannon" is a distinct cyber attack tool that hijacks traffic to or from individual IP addresses and allows China to target "any foreign computer that communicates with any China-based website," according to an analysis from information technology research group Citizen Lab of Toronto.
In March, U.S. coding site GitHub said it was deflecting most of the traffic from a days-long cyberattack that had caused intermittent outages for the social coding site, with the Wall Street Journal citing China as the source of the attack.
The attackers pushed massive amounts of traffic to GitHub by redirecting overseas users of the popular Chinese search engine Baidu Inc, according to the Journal.
GitHub supplies coding tools for developers and calls itself the world's largest code host.
The newspaper said they targeted two GitHub pages that link to copies of websites banned in China - a Mandarin-language site from the New York Times Co and Greatfire.org, which helps Chinese users circumvent government censorship.
The United States continues to work with "all willing partners" to enhance cyber security and "promote norms of acceptable state behavior," Rathke said.
Asked about reports of increasing media censorship by Chinese authorities, he said, "The United States is committed to protecting the Internet as an open platform ... free from censorship and interference."