While the group could have carried out the attacks, Mr. Zhao said the claim was probably made to blow a “trumpet for themselves.”

“It’s a way to increase their influence,” he said.

Mr. Zhao said the organization was believed to have fewer than 100 members, most of them Uighur. The Uighur are an ethnic Turkic group that once made up the majority of Xinjiang’s population. In recent decades, however, they have been edged out by China’s majority Han population, as Beijing has moved to exploit the area’s mineral resources and develop its economy.

A July 2009 protest march by Uighurs in the regional capital, Urumqi, exploded into ethnic rioting that killed nearly 200 people, most said to be Han. Government surveillance and police actions directed at Uighurs have risen sharply since then, and the area has experienced sporadic outbreaks of violence.

Many Uighurs now bridle against local restrictions on their practice of Islam, police harassment and what they say is job discrimination. China’s government says its economic development efforts have brought prosperity and jobs to Xinjiang’s Uighurs and blames outside agitators and foreign-based terrorist groups for the unrest.

The latest video shows a Uighur man identified as Memeti Tiliwaldi at what is said to be a terrorist training camp, probably somewhere in Afghanistan or in Pakistan’s lawless region near the border with China. Chinese police officials reported in early August that they had shot and killed Mr. Tiliwaldi, 29, after he was identified as one of those who staged a series of attacks in Kashgar on July 30 and 31, which left at least 18 people dead.