China Xinjiang blast killed 31 people, 90 injured: Report

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

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 station attack and other violence have been blamed on Uighur extremists, but information about events in the area, which is about 2,500 kilometers (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.