Eastern Turkistan Independence Movement (ETIM) and the Tibetan Youth Congress (TYC) are the biggest two groups in China's security concern, if you ask me.
ETIM was down for terrorist organization by the US in 2002 because of its link to al-Qaeda, by now it has committed serious enecations of civilians with bombs in 1996 and 1998 in western Xinjiang. Etim is said to have a training battalion on the Pamir, the border area between Pakistan,Tajikistan and Afghanistan. it is possible for ETIM terrorist to enter China via frontier ports for above countries.
TYC is a radical anti-China group located in Dharamsala, India, although it labels itself as nonviolent. it has 77 branches in Nepal, Bhutan, Norway, Canada, France, Japan, Taiwan, Australia, USA and in Switzerland.
TYC strongly advocates Tibetan independence with no compromise, and declared that it would use all possible means, incluing violent methods as they hinted early this year, to fight for the independence of Tibet. Tsewang Rigzin, chairman of the group told Italian Evening Post on eve of the 2008 Beijing Olympics " in order to fight against China, it's possibly time for Tibetan Resistance Movement (TRM) to take suicide violence."
TYC was involved to the Lahsa riot in March this year, as China's intelligence agency says. here's a video clip delineating the group:
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We already know that the tibetans in exile have been eager to walk across the sino-indo border in order to hold massive demonstrations against Chinese government, which was restrained by Indian Police.
I wonder if they've managed to get some Inidan passports or not, but sneak-on tibetan suicide body bombs from India might also be taken into possibility.
that's why we need also anti-terrorism cooperation from India.