Washington:  A US defence official, an ex-Boeing engineer and two others were charged with spying for China involving sensitive military and aerospace secrets, including on the space shuttle.

The four were linked to two espionage conspiracies, which the US Justice Department said posed a "grave danger" to national security.

Pentagon official Gregg William Bergersen, Chinese citizen Yu Xin Kang and Taiwan-born US citizen Tai Shen Kuo were accused of passing classified information to China, mostly pertaining to US military sales to Taiwan, according to Justice Department officials.

A Taiwan government official said on Tuesday they were trying to determine whether Tai provided Beijing with information on the island's new air defence system.

A statement from the ministry said it had set up a task force to investigate possible damage to Taiwan that spies arrested in the United States might have caused.

"We've contacted the US Defence Department ... regarding all our purchases of military and arms equipment, and the US has imposed security control measures on its internal operations," it said.

Bergersen, 51, is a weapons systems policy analyst at the Pentagon's Defence Security Cooperation Agency, which implement the US Defence Department's foreign military sales programme.

In another case, former Boeing engineer Dongfan "Greg" Chung, a China-born US citizen, was charged with stealing and turning over trade secrets also to Beijing, including the space shuttle used for US human space flight missions. Chung, 72, was also charged with economic espionage involving the C-17 military transport plane and the Delta IV rocket.

Both FBI-probed cases had a common objective: "to get a hold of our nation's military secrets," Assistant US Attorney General Kenneth Wainstein told reporters.