Urumqi, the regional capital, erupted in ethnic violence between mainly Muslim Uighurs and Han Chinese on July 5 last year.
In the following days, mobs of angry Han took to the streets looking for revenge in the worst ethnic violence that China had seen in decades. The unrest left nearly 200 dead and 1,700 injured, according to government figures.
On Monday, security personnel were concentrated in the Uighur areas of Urumqi. Armed and riot police patrolled in formation, and police vans made regular rounds in the area.
Armed police with helmets and shields also marched on the edges of People's Square in the heart of the city, where the unrest began last year. The plaza has been shut down for renovations, construction workers told AFP.
"It's really tense today. Look at the streets. There aren't many people there and normally it would be bustling at this time of day," Liu Yan, a 50-year-old Han Chinese taxi driver, told AFP.
"Uighurs, they probably don't dare to come out because it's the sensitive anniversary date."
China blamed "separatists" for orchestrating the July 2009 unrest.
But Uighurs say the violence was sparked when police cracked down on peaceful demonstrations staged over a factory brawl the month before in southern China in which two Uighur migrant workers were reportedly killed.
Authorities blocked Internet access, text messages and international phone calls in and out of Xinjiang after the riots -- restrictions that have been gradually lifted, though some Uighur-language websites remain inaccessible.
So far, about 200 people have been convicted for their roles in the violence. At least 26 of them have been sentenced to death, and nine already put to death, according to press reports.
The United States has urged Beijing to be more transparent in how it handles the court cases related to the violence.
"We have urged China to ensure that the legal rights of all Chinese citizens are respected in accordance with international standards of due process," State Department spokesman Mark Toner told AFP.
Rights watchdog Amnesty International called for an independent probe, citing "excessive use of force, mass arrests, enforced disappearances, torture and ill treatment" of prisoners during the security crackdown after the unrest.
Uighurs, a Turkic-speaking people, allege decades of Chinese oppression and unwanted Han immigration, and while standards of living have improved, Uighurs complain most of the gains go to the Han Chinese.
Tensions in the city again boiled over in September after a spate of syringe attacks -- which many victims blamed on Uighurs -- led to days of protests that left five people dead.
Authorities keen to ensure no repeat of last year's mayhem have installed 40,000 security cameras throughout Urumqi, a city of about two million people, according to state media. Anti-riot exercises have also been staged.
"As a cab driver, I would think twice before I picked up a Uighur, because I'm still scared," said Liu, though he added he counted Uighurs among his friends.
"We're still friends after the riots, though we don't meet in public anymore," the cab driver said. "We meet at their homes."
