At least 31 killed, 90 injured in attack on market in volatile western China region

May 22, 2014: In this photo released by China's Xinhua News Agency, police officers stand guard near a blast site which has been cordoned off, in downtown Urumqi, capital of northwest China's Xinjiang Uygur Autonomous Region. (AP Photo/Cao Zhiheng)

At least 31 people have died and 90 have been injured in an attack on an open-air market in the capital of Xinjiang province in western China Thursday, the latest in a series of violent incidents that the Chinese government has blamed on radical Muslim separatists.

China's state-run Xinhua News Agency said that the assailants plowed through crowds of shoppers in off-road vehicles and threw explosives out the window before crashing head-on in the attack in the city of Urumqi. The agency said one of the vehicles then exploded and quotes an eyewitness as saying there were up to a dozen blasts in all.

"I heard four or five explosions. I was very scared. I saw three or four people lying on the ground," Fang Shaoying, the owner of a small supermarket located near the scene of the blast, told the Associated Press.

The Xinjiang regional government said in a statement that the early morning attack was "a serious violent terrorist incident of a particularly vile nature."

It was not immediately clear who was responsible for the attack. Recent violence has been blamed on extremists seeking to overthrow Chinese rule in the region, which is home to the native Turkic-speaking Uighurs but has seen large inflows from China's ethnic Han majority in recent decades.

The death toll was the highest for a violent incident in Xinjiang since dayslong riots in Urumqi in 2009 between Uighurs and Hans left almost 200 people dead. Thursday's attack also was the bloodiest single act of violence in Xinjiang in recent history.

Photos from the scene posted to popular Chinese social media site Weibo showed at least three people lying in a street with a large fire in the distance giving off huge plumes of smoke. Others were sitting in the roadway in shock, with vegetables, boxes and stools strewn around them. Police in helmets and body armor were seen manning road blocks as police cars, ambulances and fire trucks arrived on the scene.

Urumqi was the scene of a bomb attack at a train station late last month that killed three people, including two attackers, and injured 79. Security in the city has been significantly tightened since that attack, which took place as Chinese President Xi Jinping was visiting the region.

In response to Thursday's attack, Xi pledged to "severely punish terrorists and spare no efforts in maintaining stability," Xinhua reported.

Public Security Minister Guo Shengkun, China's top police official, was also dispatched to Urumqi at the head of a team to investigate the incident.

In Beijing, Foreign Ministry spokesman Hong Lei said the incident "lays bare again the anti-human, anti-social and anti-civilization nature of the violent terrorists and deserves the condemnation of the world community and the Chinese people."

"The Chinese government is confident and capable of cracking down on violent terrorists. Their plots will never succeed," Hong said.

Prior to last month's train station attack, the city had been relatively quiet since the 2009 ethnic riots amid a smothering police presence. The sprawling metropolis's population of more than 3 million people is about three-fourths Han Chinese.

The station attack and other violence have been blamed on Uighur extremists, but information about events in the area, which is about 1,550 miles west of Beijing, is tightly controlled.

Tensions between Chinese and ethnic Uighurs in Xinjiang have been simmering for years, but recent attacks -- while still relatively crude -- show an audaciousness and deliberateness that wasn't present before. They are also increasingly going after civilians, rather than the police and government targets of past years.

In an unprecedented incident last year, three Uighurs rammed a vehicle into crowds in a suicide attack near the Forbidden City gate in the heart of Beijing, killing themselves and two tourists.

And in March, 29 people were slashed and stabbed to death at a train station in the southern city of Yunnan blamed on Uighur extremists bent on waging jihad.

Uighur activists say the violence is being fueled by restrictive and discriminatory policies and practices directed at Uighurs and a sense that the benefits of economic growth have largely accrued to Chinese migrants while excluding Uighurs. The knowledge that Muslims elsewhere are rising up against their governments also seems to be contributing to the increased militancy.

Thursday's attack came two days after courts in Xinjiang sentenced 39 people to prison after being convicted of crimes including organizing and leading terrorist groups, inciting ethnic hatred, ethnic discrimination and the illegal manufacturing of guns.

Among those convicted Tuesday was 25-year-old Maimaitiniyazi Aini, who received five years in prison for inciting ethnic hatred and ethnic discrimination for comments he made in six chat groups involving 1,310 people, the Supreme Court said.

In another case, a Uighur man was jailed for 15 years after he preached jihad, or holy war, to his son and another young man, according to the court.

The Associated Press contributed to this report.