"Professor Ilham has worked to promote friendship between ethnic groups and resolve conflict between them. He should not be viewed as a criminal," said the letter, emailed to AFP.
It also urged the government to review its ethnic minority policies and examine whether such policies led to the rioting.
"We ask the government that if intellectuals like Ilham Tohti, who have worked to bring together Uighurs and Han Chinese, are treated as enemies, then who are your friends?" the letter said.
According to the government, over 180 people were killed, including 137 Han Chinese, in riots that erupted on July 5 in Urumqi, the capital of China's restive Xinjiang region.
Xinjiang is home to roughly eight million Uighurs, who have complained about repression and discrimination under Chinese rule.
Tohti, a professor at the China Minorities University, was taken by police from his Beijing home last week but has not yet been charged, Tibetan activist Woeser, who also signed the letter, told AFP.
"The 158 people who have signed the open letter are only the first group to sign," Woeser said.
"A lot of people are signing the letter."
Tohti was detained after Xinjiang authorities named his blog "Uighur Online" on national television, calling it an outlet used to organise the July 5 protests in Urumqi, Reporters Without Borders said earlier.
The Public Security Bureau warned him last month his postings exploring relations between ethnic Han Chinese and Uighurs violated the law, the statement said.
The bureau would not confirm Tohti's detention when contacted by AFP last week and staff there were not available for comment on Tuesday.
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It also urged the government to review its ethnic minority policies and examine whether such policies led to the rioting.
"We ask the government that if intellectuals like Ilham Tohti, who have worked to bring together Uighurs and Han Chinese, are treated as enemies, then who are your friends?" the letter said.
According to the government, over 180 people were killed, including 137 Han Chinese, in riots that erupted on July 5 in Urumqi, the capital of China's restive Xinjiang region.
Xinjiang is home to roughly eight million Uighurs, who have complained about repression and discrimination under Chinese rule.
Tohti, a professor at the China Minorities University, was taken by police from his Beijing home last week but has not yet been charged, Tibetan activist Woeser, who also signed the letter, told AFP.
"The 158 people who have signed the open letter are only the first group to sign," Woeser said.
"A lot of people are signing the letter."
Tohti was detained after Xinjiang authorities named his blog "Uighur Online" on national television, calling it an outlet used to organise the July 5 protests in Urumqi, Reporters Without Borders said earlier.
The Public Security Bureau warned him last month his postings exploring relations between ethnic Han Chinese and Uighurs violated the law, the statement said.
The bureau would not confirm Tohti's detention when contacted by AFP last week and staff there were not available for comment on Tuesday.
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