The US, by hosting radical Uighur elements, is at least indirectly, assisting Uighur terrorism.
That aside, China should pay special attention to Syria-Turkey-Chechnya axis, because these terrorists may be receiving ideological and tactical help and training in these places.
Turkey's support for terrorism in Syria is well-documented. About Xinjiang, although the government officially does endorse terrorist groups like ETIM, there is a broad pan-Uighur establishment supported indirectly by the government.
Especially the present Turkish government, as radical and NATO-oriented as it is, may have certain members directly behind the diaspora Uighur separatism, which, provides a bridge between terrorists in Xinjiang and the host government, be it Turkey or the US.