Just over a week before the Beijing Olympics, a militant Islamic group's claims of responsibility for bombings in China have fueled unease about security. The government has assured its people and the Olympic community that heavy security will ensure a secure games. But its clampdown has smothered a broad array of groups, many with grievances against the government but without a history of violence. Among the potential troublemakers Chinese security specialists have identified are Tibetan separatists, who staged occasionally violent protests last spring; members of the banned Falun Gong spiritual movement and unemployed workers. Stirring the latest concerns were videotaped threats purporting to be from an Islamic militant group. They surfaced last week in the name of the Turkistan Islamic Party _ a group Chinese and Western terrorism experts say is an offshoot of a secessionist group from China's Central Asian frontier with ties to al-Qaida. In it, hooded men stood in camouflage fatigues with Kalashnikovs and claimed responsibility for explosions in four cities in Western China in recent months, including two bus bombings last week in Kunming city that authorities said killed two people and injured 14. One militant, identified by the Washington-based monitoring group IntelCenter as commander Seyfullah, warned athletes and spectators "particularly the Muslims" to stay away.