BEIJING, China (CNN) -- China's Foreign Ministry spokesman dismissed U.S. allegations of Chinese spying as "Cold War thinking" and said the arrests of four Chinese nationals on espionage charges were "groundless."

"We hope and we require the United States to stop (this) groundless accusation, which does not help the mutual trust, relationship and friendship between the two countries," said Liu Jianchao. "This is not the first time ... It is time for this to end."

A U.S. Justice Department official said Monday Chinese espionage was approaching "Cold War levels" after a Defense Department weapons system analyst and three Chinese nationals were arrested and charged in two espionage-related cases.

Meanwhile, in Santa Ana, California, a long-time defense industry employee and contractor was scheduled to appear in court for allegedly providing military secrets to Beijing.

"A document says he did it out of loyalty to the 'motherland'," said U.S. Attorney Thomas O'Brien.