The United States has indicted five Chinese military officials with cyber espionage charges for allegedly hacking into US companies to gain trade secrets, the Justice Department has said, publicly accusing China of cyber spying for the first time.

The department said on Monday that the hackers targeted US companies in the nuclear power, metals and solar products industries to steal information useful to competitors in China. The charges are the first-of-its-kind against state actors by the US.

China refuted the accusation, saying they were "made up". China's Foreign Ministry said that it had already protested against the indictment and urged the US to "immediately rectify mistake".

The ministry added that "so-called prosecution" would damage China-US relations and mutual trust, Reuters news agency reported.

US Attorney-General Eric Holder said that the companies targeted were Alcoa World Alumina, Westinghouse Electric Company, Allegheny Technologies, US Steel Corporation, United Steelworkers Union, and SolarWorld.

"This is a tactic the US government categorically denounces," Holder said. "Our economic security and ability to compete in the global market place are directly linked to national security."

The hackers also targeted United Steel, Paper and Forestry, Rubber, Manufacturing, Energy, Allied-Industrial and Service Workers International Union (USW), officials said.

US officials have long been concerned about hacking from abroad, especially China. Classified US State Department cables obtained by WikiLeaks traced major systems breaches to China, Reuters news agency reported in 2011.

Such charges, however, are symbolic but the move would prevent the individuals indicted from travelling to the United States or other countries that have an extradition agreement with the United States.

Last September, President Barack Obama discussed cyber security issues on the sidelines of a summit in St. Petersburg, Russia, with Chinese President Xi Jinping.

Source: Reuters And AP