Ting Yu-chou, former secretary general of Taiwan's National Security Council, said the island's plans for repelling invading forces needed to be entirely re-thought following the arrest of a senior communications operative on charges of spying for Beijing.

Taiwanese military brass have been scrambling to contain the possible fallout since Major General Lo Hsien-che was arrested last month.

The 51-year-old was in charge of the army's telecommunications and electronic information department. Reports said he would have had access to highly sensitive information of great value to the mainland.

"Since I have ever served as the army commander-in-chief, military intelligence chief and National Security Bureau chief before, I fully understand the importance of Lo's position," Ting told the Taipei-based China Times.

"The worst damage wrought by Lo could be on the army's defence operation plans," he said.

Ting said "Lo was deeply involved in Taiwan's military wargames and supposed to be familiar with the island's countermeasures against the Chinese communists".

Although Taiwan's defence ministry said it was not immediately clear how much harm Lo had caused Taiwan's military, Ting urged the defence ministry "to prepare for the worst".

"The army's defence operation plans, from the codename to the content, must be revised."

Local media said prosecutors had seized highly confidential documents while searching Lo's office.

Some reportedly detail the Po Sheng (Broad Victory) system, a sophisticated command, control and communications network that Taiwan is purchasing from US defence contractor Lockheed Martin at a cost of Tw$46 billion ($1.6 billion).

China is believed to be very interested in learning more about the project, which gives the Taiwanese military some access to US intelligence systems, the China Times said.

Other documents include the army's procurement of 30 Boeing-made Apache AH-64D Longbow attack helicopters and the army's underground optical fibre network system, it said.

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

Beijing still regards the island as part of its territory awaiting reunification, and refuses to renounce the possible use of force despite the fast warming ties between Taipei and Beijing.