Four Taiwan civil servants filmed visiting hostess bars in neighbouring China have been blackmailed into becoming spies for Beijing, the government of the self-ruled island said today.

Four civil servants on trips to China were filmed in hostess lounges and then blackmailed into becoming informants for Beijing, Taiwan Justice Ministry spokesman Luo Chi-wang said. He did not say what has happened to them since being uncovered.

Another 36 conducted themselves in "inappropriate ways" with Chinese officials, he said without elaborating.

China's Taiwan Affairs Council said it did not know about the case and could not comment.

Communist China has claimed democratic Taiwan since 1949, when Mao Zedong's forces won the Chinese civil war and Chiang Kai-shek's Nationalists (KMT) fled to the island. Beijing has vowed to bring Taiwan under its rule, by force if necessary.

But since China-friendly President Ma Ying-jeou took office in Taiwan last May, relations have improved quickly, increasing the frequency of high-level visits between the two sides.

Last month, a Taiwan presidential office employee was arrested on suspicion of leaking secrets to Beijing, indicating the distrust that lingers between the two old foes.

The Justice Ministry said it had sent a letter to all government departments warning them to be careful.

"There have been some cases in the past, so we wanted to send a letter giving direction," a section chief in the ministry said. "Perhaps they need to pay more attention to their own actions and be careful not to fall into traps."