BEIJING, China (CNN) -- Thousands of Chinese demonstrators crowded the streets of Urumqi in western China on Thursday to protest what they say is a lack of police protection, witnesses said.

Chinese soldiers have been recently deployed on the streets of Urumqi in northwest China.

Over the past month, more than 400 ethnic majority Han Chinese have been stabbed with tainted syringes by Uyghurs, the Muslim minority, according to local news reports. The stabbings fueled Thursday's protests by Han Chinese in the capital of China's Xinjiang Uyghur Autonomous Region.

Many of those attacked with the hypodermic needles were hospitalized, but there have been no reports of deaths, the reports said.

Fifteen suspects have been detained for allegedly carrying out the stabbings, a senior official said Wednesday, according to China's state-run Xinhua news agency. Of the 15, four have been formally charged, Xinhua reported.

A source told CNN that "countless" police and soldiers have deployed to Urumqi and so far, the demonstrations have been peaceful.

A local woman told CNN that the stabbings were ethnically motivated and that government text messages to citizens have warned that the syringes contained an unknown disease.

Ethnic-fueled violence between the Han Chinese and Uyghurs has plagued Urumqi since July, when soldiers and police stormed the streets to quell riots. Unconfirmed reports of deaths in those riots range from 200 to many more. Watch a report on the alleged attacks »

An art gallery director in Urumqi told CNN that thousands of people gathered on the streets on Thursday.

"People are protesting here right now. It's all Han people," he said, declining to give his name because of safety reasons. "Since August 3, the Uyghurs have been stabbing the Hans with needles with an unknown virus. People are all very scared."

A spokeswoman for China's Foreign Ministry said she did not know about the protests.

"I have not yet received news of this, but the Chinese government is capable of upholding stability and social unity," Jiang Yu said.

A receptionist at a bank in the area also told CNN about the protests.

"I heard that today, even during the protest, some people got stabbed, too. People are angry that the government is not doing much against the Uyghurs' needle stabbing," said the woman, who also was afraid to give her name.

All About China • Xinjiang Uygur Autonomous Region