The daughter of a prominent Uighur academic told US lawmakers Tuesday that his arrest sent a message China will not tolerate even peaceful expression of grievances by the minority group.

Ilham Tohti, an economist in Beijing who has been one of the most visible critics of China's treatment of the mostly Muslim ethnic group, was detained in January and accused of separatism, a charge that could carry the death penalty.

His 19-year-old daughter Jewher Ilham, who studies in the United States, told a hearing in the US Congress that her father was not a separatist and opposed violence.

"In fact, he is exactly the sort of person a rational Chinese political structure would seek to engage with in order to address the conditions of the Uighur people," she told the Congressional-Executive Commission on China, which looks at human rights.

"By arresting my father and threatening him with charges that carry the severest of penalties, it has driven many Uighurs to a point where they can't even imagine that their wholly justified grievances can get any sort of hearing under Chinese rule," she said.

Ilham said that she has had no news on her father's condition and voiced concern for her family, which she said was under 24-hour surveillance with as many as eight security officers outside their home.

Ilham said that her seven-year-old brother was suffering nightmares and her stepmother, also an academic, fears that she will lose work when her contract expires in May.

Ilham, who spoke with poise from a prepared statement in English, said she had initially planned to join her father for just one month as he took a one-year position at Indiana University starting in February 2013.

But Tohti was stopped at a Beijing airport from going to the United States and Ilham went alone after what she said was a bureaucratic error. She has been studying English at Indiana University ever since.

The United States and European Union have condemned Tohti's detention. China has said it has "irrefutable proof" against him.

- Broader crackdown -

Uighurs, concentrated in the western region of Xinjiang, frequently charge that their political and religious rights are stifled by China.

Xinjiang has been hit by periodic unrest. Chinese authorities charged that Uighur separatists carried out a machete attack last month in the southwestern city of Kunming that killed 29 people in what state media has described as "China's 9/11."

Senator Sherrod Brown, who chaired the hearing, voiced concern over growing arrests of activists, intellectuals and journalists in China since President Xi Jinping assumed power last year.

"China's government has shown little tolerance for independent voices, even those that echo the government's concerns and try to uphold the law," said Brown, a member of President Barack Obama's Democratic Party.

Teng Biao, a leading human rights lawyer who has previously run afoul of Chinese authorities, told the hearing by video link that a number of prisoners have been tortured.

He voiced alarm over the recent death in custody of activist Cao Shunli, who according to her family and lawyers was deprived of medical care. China has denied wrongdoing.

"Under the guise of maintaining stability above all, the authorities brutally punish anyone who in their mind dares to threaten their legitimacy to rule China," he said from Hong Kong.