China's state-controlled media have warned citizens to raise their awareness and prevent leakage of state secrets, charging that illegal surveys by foreigners in the country were on the rise and threatening national security.

Many Chinese mistakenly believe that geographic information is not secret because satellites are commonly used to gather such information, the English-language China Daily said on Wednesday, quoting the Chinese-language tabloid Global Times.

But coordinates, topography and geologic information of key areas and core facilities are still top secret. Once acquired by other countries, the information could be used to attack wartime targets, the China Daily said, citing experts.

Some overseas organizations had taken advantage of local governments' eagerness to attract foreign investment and directly asked for geographic information, the newspaper said.

Others used the cover of setting up joint ventures and cooperative projects, it added.

China's State Bureau of Surveying and Mapping has warned that foreigners who carried out illegal surveys or published such data without permission would face severe punishment. In April and May, two Taiwanese were prosecuted for drawing and selling overseas maps of China including a large amount of top secret information about public security facilities, the China Daily said.

In another case, a foreign map company with strong government connections was caught in May 2004 when it entered a military area in the eastern coastal province of Shandong, it said.

Their surveys included accurate positioning of Chinese armies and detailed information on communication facilities in eastern and southern China, the daily said.

This month, authorities banned the Chinese edition of China Development Brief, a newsletter published by a Beijing-based Briton which reports about China's environment and civil society, for conducting unauthorized surveys.

Last year, two Japanese scholars conducting unauthorized research in China's far west Xinjiang region were deported.