WASHINGTON (Reuters) -The U.S. warned on Tuesday that Chinese intelligence was using deceptive methods to target current and former U.S. government employees for recruitment.

The warning from the National Counterintelligence and Security Center comes amid mass federal firings led by Elon Musk's Department of Government of Efficiency.

"Foreign intelligence entities, particularly those in China, are targeting current and former U.S. government (USG) employees for recruitment by posing as consulting firms, corporate headhunters, think tanks, and other entities on social and professional networking sites," the center said in a bulletin.

The center said deceptive online job offers and other approaches have become more sophisticated in targeting individuals with U.S. government backgrounds seeking new employment. It warned current and former federal employees of such approaches.

It added that clearance holders were obligated to protect classified data even after leaving federal employment.

The Chinese foreign ministry said on Wednesday it was not aware of the situation and accused the U.S. of spying on China.

Reuters previously reported about a network of companies operated by a secretive Chinese tech firm that had been trying to recruit recently laid-off U.S. government workers.

(Reporting by Jasper Ward, additional reporting by Eduardo Baptista in Beijing; Editing by Stephen Coates and Kate Mayberry)