The US has charged five Chinese army officers with hacking into private-sector American companies in a bid for competitive advantage, in the first cyber-espionage case of its kind.

Attorney General Eric Holder said the alleged breaches were "significant" and demanded "an aggressive response".

US prosecutors say the officers stole trade secrets and internal documents from five companies and a labour union.

China denied the charges and warned the case would harm US-China relations.

In Washington on Monday, Mr Holder said the hacking charges laid against the Chinese nationals were the first against "known state actors for infiltrating US commercial targets by cyber means".

He identified the alleged victims as Westinghouse Electric, US Steel, Alcoa Inc, Allegheny Technologies, SolarWorld and the US Steelworkers Union.

"The alleged hacking appears to have been conducted for no reason other than to advantage state-owned companies and other interests in China, at the expense of businesses here in the United States," Mr Holder said.

In response, the Chinese government said its "stance on the issue of internet security is consistent and clear".

Foreign ministry spokesman Qin Gang said the allegations were "made up" and would "damage Sino-American cooperation and mutual trust".

"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," he said.