Prominent Chinese intellectuals and writers have signed a petition calling for the release of a well-known ethnic Uighur economist in Beijing who was apparently detained last week during a bloody outbreak of ethnic violence in western China. The economist, Ilham Tohti, 39, who had written critically about government policies toward the Uighurs, is the best known person to be detained so far in relation to the ethnic strife. Tohti, a professor at the Central University for Nationalities, vanished from his Beijing home sometime last week and made a call to a friend to say he would be detained. Tohti ran a Web site called Uighur Online, which had become a popular forum for discussion of issues important to the Uighurs, a Turkic-speaking ethnic group of mostly Sunni Muslims that is the largest in oil-rich Xinjiang, China's biggest administrative region. The site is now blocked in China. Ethnic tensions between the Uighurs and the Han, the dominant ethnic group in China, exploded last week after a Uighur protest on July 5 in Urumqi, the capital of Xinjiang, turned violent when riot police officers tried to halt the rally. Uighur mobs rampaged through the city, killing many Han civilians and setting fire to cars and buildings. For days afterward, Han mobs with sticks and knives attacked and killed Uighurs. The government says at least 184 people were killed and 1,680 injured, the vast majority being Han. But many Uighurs in Urumqi say that count does not include hundreds of Uighurs killed by security forces or by Han vigilantes. The state news agency reported Monday that police officers shot dead two armed Uighurs and wounded a third. On July 6, Nur Bekri, the governor of Xinjiang, said in a speech that Uighur Online had helped instigate the rioting by spreading rumors. Chinese officials insist that Uighurs abroad and some inside China were responsible for starting the violence. The officials avoid any discussion of systemic problems in Xinjiang that have led to deep-rooted resentment among many Uighurs: the large numbers of Han migrating to Xinjiang in the past decades and taking jobs, for example, or the restrictions on religious practice. Tohti had been increasingly critical of the lack of jobs for Uighurs and policies that encouraged the influx of Han settlers. 'Unemployment among Uighurs is among the highest in the world,' he said in an interview in March with Radio Free Asia, which is supported by the U.S. government. While doing research for the Chinese government at one point in the 1990s, Tohti said, he discovered that there were 1.5 million unemployed workers in Xinjiang. The petition to free Tohti was started by Wang Lixiong, one of China's leading experts on ethnic minority issues and the husband of Woeser, a well-known Tibetan blogger. The petition had 158 signatures early Wednesday. The signers are mostly ethnic Han and from all over China. One of the signers, Ran Yunfei, a well-known magazine editor and blogger who is of Monguor, or Tu, ethnicity, said in a telephone interview: 'Even if we don't have democracy, we should have freedom of speech. And they should not detain someone for his remarks. As far as I know, Professor Ilham's Web site is a very gentle and rational one.' In the radio interview in March, Tohti said he was concerned about being imprisoned for his writings. 'Of course I worry, but what I have said doesn't conflict with Chinese law,' he said. 'If they put me in jail, I am ready. I've sat in front of a computer for so many years. Jail would give me a chance to exercise and lose weight.' 