Liu Yaohua stressed that it was a "man-made" explosion, without saying it was caused by a bomb.
Francesco Sisci is the Beijing-based editor for the Italian newspaper "La Stampa." He told RFE/RL that Chinese media outlets have done little reporting on the blast. "We are not officially sure it is a bomb," he said. "The Chinese media reported today, very briefly, this explosion. We have few details."
The blast reportedly ripped through a minibus as it was traveling along a highway between the cities of Karamay and Usu in northern Xinjiang, some 200 kilometers from the Kazakh border. Xinhua reported that nine people died instantly and two others died later in hospital.
Sisci noted that blasts caused by the careless handling of explosives and other hazardous materials are common in China, despite laws against possessing or carrying them on public transport. "Explosions in China are fairly common because explosives are carried all over the place and used for a variety of reasons -- from mining to fireworks," he said. "They are quite commonly purchased, everywhere."
However, the French news agency AFP quoted unnamed Chinese officials as saying they cannot rule out the possibility that the blast is linked to Muslim separatists of the Muslim Uyghur minority group.
Marc Allison works for the China research team at the human rights watchdog Amnesty International in London. "China is all too ready to blame any act of violence or even acts of peaceful opposition in Xinjiang on so-called 'separatists' or 'terrorists,'" he told RFE/RL. "Thousands of Uyghurs have been imprisoned and some of them executed because they've been accused of such crimes."
The Chinese government blames "terrorists" for some 200 incidents in Xinjiang from 1990 to 2001 that left 162 people dead, including nine killed in three bus bombings in Urumqi in 1997.
Allison questioned the basis of convictions in such cases. He noted that investigations by Chinese authorities, and subsequent trials, are conducted in secret, while defendants do not have adequate access to defense lawyers.
He said all of this is happening in an atmosphere of "very tight repression" of the Uyghur minority. "Any expression of independent Uyghur identity, including teaching the Koran to children or promoting greater autonomy for the region, regularly leads to arrests, torture, and imprisonment," Allison said.
Turkic-speaking Uyghur separatists have been fighting to reestablish an independent state of East Turkestan in today's Xinjiang. They accuse the ruling Chinese of political, religious, and cultural repression.