A senior Taiwanese military officer who served at the island's de facto US embassy has been placed under investigation after failing a lie detector test, the defence ministry said Monday.

From late 2012, all Taiwan's defence attaches serving abroad have had to take a lie detector test, a move designed to stem a wave of military espionage cases, usually involving arch-rival China.

"He failed to pass the test, and we've been trying to clarify (some suspicions)," defence ministry spokesman David Lo told AFP.

Major General Li Hsien-sheng, who took the mandatory polygraph after finishing a two-year posting in May, was quoted as saying he was "not afraid" of the inquiry by local media, and told the United Daily News: "I believe I will get through this investigation."

Taiwan authorities in January 2011 arrested Major General Lo Hsien-che over claims that he spied for China, after he was lured by sex and money offered by a female Chinese agent on a 2002-2005 posting to Thailand.

Lo Hsien-che was head of the army's telecommunications and electronic information department.

Taiwan and China have spied on each other ever since they split in 1949 at the end of a civil war.

Relations have improved markedly since President Ma Ying-jeou of the China-friendly Kuomintang came to power in 2008 on a platform of strengthening trade and tourism links.

But Beijing still regards the island as part of its territory awaiting reunification, by force if necessary.

Washington switched diplomatic recognition from Taipei to Beijing in 1979.