Hundreds of Han Chinese armed with clubs marched through the Xinjiang capital of Urumqi, knocking over food stalls run by Muslims. Police used loudspeakers Tuesday to appeal to the marchers to stop, but about 300 of them were marching down a street about four blocks from People's Square, the starting point of Sunday's riot that left 156 dead. The crowd waved their wooden sticks, lead pipes, shovels and hoes in the air as they marched. As they headed down a back street toward a mosque, several loud explosions rang out followed by rising white puffs of smoke - possibly tear gas that anti-riot squads have used in previous days. Security forces have clamped down on the city of Urumqi and set up checkpoints to catch any fleeing rioters, state media reported, after tensions between ethnic Muslim Uighur people and China's Han majority erupted into riots. On Sunday, rioters overturned barricades, attacking vehicles and houses, and clashed violently with police, according to media and witness accounts. State television aired footage showing protesters attacking and kicking people on the ground. Other people, who appeared to be Han Chinese, sat dazed with blood pouring down their faces. There has been little information about how so many people died. The government blamed Uighur exiles for stoking the unrest. Exile groups said the violence started only after police began violently cracking down on a peaceful protest. Thousands of people had gathered Sunday in the regional capital for the protest that apparently spun out of control. Accounts differed over what happened, but the violence seemed to have started when the crowd of protesters refused to disperse. The official Xinhua News Agency reported hundreds of people were arrested. Mobile phone service provided by at least one company was cut Monday to stop people from organizing further action in Xinjiang. The demonstrators had been demanding justice for two Uighurs killed last month during a fight with Han Chinese co-workers at a factory in southern China. Tensions between Uighurs and the majority Han Chinese are never far from the surface in Xinjiang, China's vast Central Asian buffer province, where militant Uighurs have waged a sporadic, violent separatist campaign.