Resuming cyber security cooperation between China and the United States would be difficult because of "mistaken US practices", China's top diplomat told US Secretary of State John Kerry.

Cyber security is an irritant to bilateral ties. On Wednesday the US Federal Bureau of Investigation said hackers it believed were backed by the Chinese government had launched more attacks on US companies, a charge China rejected as unfounded.

In May, the United States charged five Chinese military officers with hacking American firms, prompting China to shut down a bilateral working group on cyber security.

Yang Jiechi, a state councillor overseeing foreign affairs, told Kerry in Boston the United States "should take positive action to create necessary conditions for bilateral cyber security dialogue and cooperation to resume", according to a statement seen on the Chinese Foreign Ministry website on Sunday.

"Due to mistaken US practices, it is difficult at this juncture to resume Sino-US cyber security dialogue and cooperation," Yang was quoted as saying. The statement did not elaborate.

Former US spy agency contractor Edward Snowden has said the US National Security Agency hacked into official network infrastructure at universities in China and Hong Kong.

China, repeatedly accused by the United States of hacking, has used Snowden's allegations as ammunition to point the finger at Washington for hypocrisy.