Public Security Ministry spokesman Wu Heping said the attacks were planned for last year, after long-simmering tensions between Uighurs and majority Han Chinese migrants turned deadly in the regional capital Urumqi last July 5.
Nearly 200 people died in the violence Beijing accuses overseas organizers of plotting.
He said authorities had busted a gang of more than 10 "hardcore terrorists" linked to the East Turkestan Islamic Movement, a banned terrorist organization advocating independence for Xinjiang.
"The uncovering of this major terrorist group again proves that the ETIM and other terrorist organizations constitute the gravest terrorist threat that our nation faces at this present time and in the future," Wu said at a media briefing.
Wu said the gang had assembled bombs, pipe bombs and gasoline bombs, knives and other materials and had planned attacks in southern Xinjiang cities between July and October 2009. The plot was discovered, and the gang members fled, most to different parts of China and three abroad, Wu said.
Though he did not identify where the three fled, Wu said they were deported to China in December. That same month, Cambodia repatriated 20 Uighurs it said had illegally entered the country, touching off an international outcry.
During the briefing, several slides were displayed showing what appeared to be pipe bombs made from black powder and ball-bearings. Another showed a minivan and four-wheel drive vehicles allegedly used by the gang, while a third showed a kitchen-like room described as a bomb factory in Xinjiang.
No reason was given why the announcement was made now, but it comes just before the first anniversary of the unrest.
The rioting last July between Muslim Uighurs and members of China's Han majority was the worst communal violence to hit Xinjiang in more than a decade, but authorities have for decades battled a simmering rebellion. Uighurs' resentment has been fueled by what many see as Beijing's heavy-handed controls on religion and policies that favor the Han Chinese migrants flooding their traditional homeland.