Five members of the Chinese military are charged with hacking into private-sector American companies and allegedly stealing state secrets, the US Justice Department says.

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In the first of its kind, China was accused of spying on companies in the nuclear power, metals and solar products industries, in a bid to compete with the country's state-owned enterprises.

Six American companies, including United States Steel Corp, Alcoa Inc and Allegheny Technologies Inc, and one trade union were victims of Chinese hacking attacks, US officials said.

However, the Chinese Foreign Ministry issued a strongly-worded statement, saying the US grand jury indictment was "made up" and would "damage Sino-American cooperation and mutual trust".

"The Chinese government's stance on the issue of Internet security is consistent and clear," said the statement from Foreign Ministry spokesman Qin Gang, which urged "immediate rectification".

"China is a staunch defender of network security, and the Chinese government, military and associated personnel have never engaged in online theft of trade secrets," the statement said. It added that it was suspending activities of the Sino-US internet working group.