Urumqi, China ? Chinese leaders bowed to public demands and sacked the head of a western city wracked by communal violence and a bizarre string of needle attacks, hoping to calm uneasy mobs and end protests that percolated for a third day Saturday.

The removal of Urumqi’s Communist Party Secretary Li Zhi came amid reports of police again dispersing crowds outside Urumqi’s government offices using tear gas, and more unconfirmed reports of needle attacks, including one on an 11-year-old boy in a downtown square.

The city’s chief prosecutor announced further details about four people arrested over the attacks, but offered little to back up the government’s claims that they were an organized campaign to spread terror.

Protesters marched by the thousands Thursday and Friday demanding the resignation of Li and his boss, Xinjiang party secretary Wang Lequan, for failing to provide adequate public safety in the city. Also sacked was the police chief of Xinjiang, China’s westernmost region that abuts Central Asia and whose capital is Urumqi.

An Urumqi government spokeswoman and the official Xinhua News Agency gave no reasons in announcing the changes. But July’s riot was the worst communal violence in more than a decade in Xinjiang — where Uighur separatists have waged a sporadically violent campaign for a homeland. The renewed protests this week underscored the difficulties authorities were having in reasserting control.

The firing may also help quash calls to dismiss Wang — a member of the country’s ruling Politburo and an ally of President Hu Jintao.

“I would say that this is the sacrificial lamb,” Russell Leigh Moses, an analyst of Chinese politics based in Beijing. “But it will be interesting to see what the reaction in the streets is and whether this satisfies people’s anger or not.”

Li, a 58-year-old career official in Xinjiang, played a visible role during the July violence and recent protests. In July he climbed atop a car with a megaphone and urged an angry crowd of Han Chinese to show their patriotism by fighting separatists but not ordinary Uighurs.

On Thursday, when more than 10,000 people protested through the city, Li and Wang separately waded into crowds to meet with protesters to defuse tensions, only to be greeted with shouts to “step down.”