China must "take serious steps" to fight hacking of U.S tech networks, the Obama administration said on Monday.
National Security Adviser Tom Donilon said the sophisticated intrusions aimed mostly at business were a potential risk to U.S.-China relations.
But the senior official balanced his pointed comments with an appeal to Beijing to begin a constructive dialogue on efforts to address cybersecurity globally.
"The United States will do all it must to protect our national networks, critical infrastructure, and our valuable public and private sector property," Donilon told the Asia Society in New York.
Donilon said that American business is speaking out about its concerns with "sophisticated, targeted theft of confidential" information and "proprietary technologies through cyber intrusions emanating from China on an unprecedented scale."
Virginia-based Mandiant published a report last month alleging the Chinese government was sponsoring cyber-espionage against top U.S. companies.
China dismissed the charges, insisting that it was the victim of many cyber attacks - most originating in the United States.
But another report from Akamai Technologies, an Internet services company, said a third of all observed computer attacks from July through September last year came from China.
The United States was second, originating 13% of observed attacks, followed by Russia with 4.7%.
The Justice Department and FBI have pledged to crack down on hacking, are advising companies on how to beef up their security, and have proposed to better coordinate efforts with allies to prosecute foreign hackers.
"The international community cannot afford to tolerate such activity from any country," Donilon said.
His language was the most direct yet from the Obama administration on the China-hacking link, although officials have gradually increased the sharpness of their rhetoric.
He said the U.S. government wants China to recognize "the urgency and scope" of the cybersecurity issue and "the risk it poses" to international trade and to the "reputation of Chinese industry and to our overall relations."
The Obama administration also wants Beijing to "take serious steps to investigate and put a stop to these activities."
Finally, he said, the United States wants China to engage "with us in a constructive direct dialogue to establish acceptable norms of behavior in cyberspace."
In February, Attorney General Eric Holder suggested cyber attacks overall are more pervasive than most companies realize.
President Barack Obama said in his State of the Union address that increasing the nation's cyber security is among his second term priorities.