China said Thursday claims that a Chinese agent had been involved in espionage carried out by a US defence official were "totally made up."

The Chinese statement came a day after US officials said a senior Pentagon employee had been charged with conspiracy to pass classified information to an agent of China.

"Those accusations that China is spying in the United States are totally made up," foreign ministry spokesman Ma Zhaoxu told reporters in Beijing.

"We urge the United States to abandon its Cold War mentality, stop its groundless accusations against China and do more to help mutual trust between the United States and China and the friendship between the people."

Retired air force Lieutenant Colonel James Wilbur Fondren, a deputy director of the US Pacific Command's Washington Liaison Office, became the fourth person targeted after a Chinese espionage ring was unmasked last year.

Dana Boente, acting US attorney for the Eastern District of Virginia, said Wednesday "providing classified information to a foreign agent of the People's Republic of China is a real and serious threat to our national security."

The US government accuses China of mounting an aggressive operation to prise open its secrets, and President Barack Obama is weighing an overhaul of cyber-security after several reports of computer hacking originating in China.