Amnesty International on Tuesday slammed an ongoing crackdown on mainly Muslim Uighurs in China's far-western Xinjiang, as authorities vowed stability two years after deadly riots rocked the region.

More than 200 people were killed and 1,700 injured -- according to official figures -- when street battles between ethnic Han Chinese and Muslim Uighurs exploded in Xinjiang's capital Urumqi on July 5, 2009.

The unrest, which lasted for days, was largely fuelled by Uighur resentment over China's rule of Xinjiang and marked the worst ethnic violence that the country had seen in decades.

According to Amnesty, hundreds of people have been detained and prosecuted since the riots, with several dozen sentenced to death or executed and many more sentenced to long prison terms.

"The government is not only still muzzling people who speak out about July 2009, it is using its influence outside its borders to shut them up," Sam Zarifi, Amnesty Internationals director for Asia-Pacific, said in a statement.

"The general trend towards repression that we see all over China is particularly pronounced in Xinjiang, where the Uighur population has become a minority in its own homeland."

Managers of well-known Uighur websites and journalists have been jailed for posting messages on the protests, or for talking to foreign media, while Beijing has sought the repatriation of those believed to be involved in the unrest from neighbouring Central Asian states, Amnesty said.

The Germany-based World Uighur Congress also denounced the ongoing crackdown and demanded that Beijing allow an independent investigation into the riots and account for all those killed, jailed or executed.

"For many years, the Chinese government has waged an intense and often brutal campaign to repress all forms of Uighur dissent, cracking down on Uighurs' peaceful political, social and religious activities and independent expressions of ethnicity," the group said.

Locals in Urumqi, when contacted from Beijing, said the situation appeared normal on Tuesday, though there was an increased police presence in the city.

Authorities continue to blame "separatists" for the July 2009 unrest.

"We must be self-conscious while standing in the front lines of the anti-separatist struggle and never waver in maintaining the overall political stability of Xinjiang," the region's top Communist Party leader Zhang Chunxian said in remarks posted on his government's website Monday.

"We must always maintain clearheadedness and deeply acknowledge the extremely important and urgent nature of safeguarding stability in Xinjiang."

Zhang appeared late Monday at a street market in the Uighur section of Urumqi and chatted with locals, Xinhua news agency said.

China's foreign ministry spokesman Hong Lei on Tuesday defended the government's crackdown, saying the unrest in Xinjiang was organised by terrorists, separatists and religious extremists inside and outside of China.

"The Chinese government, in order to maintain stability and national solidarity, has severely punished the criminals involved in the incident," Hong told reporters.

"At the moment, the society in Xinjiang is stable, the economy is developing and all ethnic groups are living in harmony together."