Chinese Muslim militants have been to Taliban-controlled parts of neighboring Pakistan and Afghanistan, but there is scant evidence supporting Chinese government claims that they returned home to carry out recent terrorist attacks.
Overseas analysts and Uighur activists call the Chinese accusations a smoke screen to obscure the anger and hopelessness among Muslim ethnic Uighurs in the Xinjiang region they say are driving the violence.
Violence in Xinjiang poses a challenge to China's development plans in the resource-rich region, as well as Beijing's contention that its policies toward ethnic minorities are successful. By blaming outside forces it avoids having to acknowledge shortcomings in those policies.
Authorities have pledged to increase pressure further in the far-western region, ordering a sweeping security clampdown and vowing "no mercy" toward anyone accused of violence or separatism.
"Those criminals who dare test the law with their persons and carry out violent terrorist acts, we will punish harshly, showing no mercy and never being soft," Public Security Minister Meng Jianzhu was quoted as telling participants at an anti-terrorism conference Thursday in the regional capital of Urumqi.
Such high-pressure tactics routinely backfire by increasing anger and hopelessness among Uighurs and pushing them closer to extremism, said Dilxat Raxit, spokesman for the German-based World Uyghur Congress.
Uighurs (pronounced WEE-gurs), are culturally, linguistically and religiously distinct from China's Han ethnic majority, and share many links with the native populations of Kazakhstan, Uzbekistan and other parts of Central Asia. Many deeply resent the Han Chinese majority as interlopers and see mass migration to the region as dooming them to minority status in their own homeland. A low-intensity separatist movement has existed for decades, but recent years appear to have ushered in an upsurge in violence.
"People will start to lose all hope and become more likely to make the wrong choices," Raxit said.
Such desperation boils over every summer, most recently in southern Xinjiang, where Uighurs predominate.
At least three dozen people, including the alleged perpetrators, were killed in three attacks in recent weeks in the cities of Hotan and Kashgar.
Those came despite a massive security presence that was tightened following a major anti-Chinese riot in Urumqi two years ago in which at least 197 people were killed.
Beijing blames the violence on militants based overseas, specifically ones from the East Turkistan Islamic Movement who it says trained in militant camps in Pakistan. China's naming of its longtime ally is seen as a move to bolster its claims and perhaps push Islamabad to increase pressure on militants within its borders.
Yet Beijing has provided no direct evidence, and analysts say they suspect its claims are driven more by ideology than proof.
"I don't think there is any reason to assume that any organization is orchestrating. Barring any evidence, it's ridiculous to make such a claim," said Dru Gladney, an expert on Xinjiang politics at the Pacific Basin Institute at Pomona College in California.
Gladney and other experts even question whether the ETIM still operates in any coherent form. While the U.S. listed the group in 2002 as a foreign terrorist organization, that was seen mainly as a calculated move to win Beijing's support in the United Nations against Iraq.
After years of controversy, the group was quietly removed from the terrorist list last year.
"I have seen no irrefutable evidence that ETIM still exists ... or that it is responsible for the recent round of violence," said Gardner Bovingdon, a professor of Central Asian studies at Indiana University and the author of a history of the Uighur struggle.
That Uighurs have fled across the border to Pakistan and Afghanistan is not disputed. More than a dozen have been captured and sent to Guantanamo Bay, while 13 Uighurs were reportedly killed by a U.S. airstrike in northwestern Afghanistan last year. Pakistani intelligence officials and Taliban fighters have also confirmed the presence of Chinese Muslims in Taliban-controlled areas of Pakistan, saying they stand out for their lack of a common language with other militants and their relative ignorance of radical Islam.
There are thought to be 100 to 150 Uighur militants in Pakistan's northwest, most of them in the North Waziristan tribal region, said Mohammed Amir Rana, a Pakistani expert on militancy. They are part of a mix of Pakistani extremists and hundreds from elsewhere in the world.
"One thing is clear, these Uighurs are mixed up with other militants. It will be very difficult to just target them, how can they be isolated?" Rana said.
Compared to the violence in Pakistan and Afghanistan, the recent Xinjiang attacks have shown little sophistication, using knifes and makeshift weapons such as hijacked trucks and gasoline bombs instead of high explosives or automatic rifles. Restaurants and shops are the usual targets rather than government or military installations or infrastructure such as railway lines.
Backing the government's claims, counterterrorism expert Li Wei, director of the Center for Counterterrorism Studies, which has ties to China's spy agency, said Uighur militants based in northwestern Pakistan smuggled recruits and trained insurgents across the border in concert with multinational crime syndicates.
Li said militants are also active on the Internet, spreading radicalism and offering instruction in bomb making and other terrorist skills. He declined to disclose his sources.
He said the increased violence represents renewed desperation by militants who fear losing Uighur sympathy due to successful government policies.
"Since Xinjiang is developing so fast and the people's living conditions are significantly improved, the point in supporting them will cease to be valid and they will lose support," Li said, echoing government assertions that economic development is the answer to the region's problems.
Overseas Uighur activists and analysts say the reason for attacks is just the opposite, that Uighurs feel increasingly disenfranchised by government economic policies and angry over tightened restrictions on their culture, religion, and language _ complaints similar to those voiced by the indigenous populations of Tibet and Inner Mongolia where protests have also occurred.
Since the Urumqi riot, policies have become more draconian, according to Uighur activists. Mosque attendance is restricted, with children, students, and government employees barred altogether; beards and veils are discouraged or banned outright; fasting during the month of Ramadan is prohibited for many; and Chinese is replacing the Uighur language in schools and offices.
Associated Press writer Chris Brummitt in Islamabad contributed to this report.