CHINESE state security agents began tracking American air force personnel Joseph Chan and Dwayne Florenzie soon after they entered China on July 23, diplomatic sources in Beijing said.
The two liaison officers had informed Chinese authorities of their plans to travel on the mainland, as is required of military personnel attached to the US Consulate-General in Hong Kong.
Sources said army officers and diplomats attached to Western and some Asian consulates in Hong Kong began 'fact-finding trips' to China several years ago.
This enabled diplomats and officers to get a first-hand feel of domestic politics, including army developments.
'The diplomatic personnel are usually only interested in information they can get from published sources, or from talking to local people,' a source said.
'If they have a military orientation, their fact-finding is usually restricted to copying down licence plate numbers, observing the density of military traffic, and assessing whether army and police officers are on alert.
'Their governments will not assign them to sensitive jobs such as intelligence-gathering since they are not accredited with Beijing,' the source said.