A prominent Uighur academic sentenced to life in prison called Wednesday for "peace", his lawyer said, as China hit back at western powers which accused it of silencing a moderate voice.

Analysts say the sentencing of Ilham Tohti -- a persistent but moderate government critic who spoke out for the rights of the mostly-Muslim Uighur minority -- on charges of "separatism" risks inflaming tensions in the restive Xinjiang region.

"Peace is a gift from the heavens to Uighurs and Han (China's majority race)," Tohti said from prison, his lawyer Li Fangping told AFP. "Only with peace and kindness can we create a better common environment."

Li said Tohti has been forced to wear painful leg irons and is confined to his cell 24 hours a day with six convicts found guilty of crimes including drug dealing, rape and murder.

"I am brave and I won't be weak," Tohti said, according to Li.

The court's decision -- which includes the confiscation of all his personal property -- has been seen as unusually harsh, and comes amid a broader crackdown on what the state claims is a terror-backed independence movement in Xinjiang.

The sentencing of the 44-year-old drew strong condemnation from the United States and European Union (EU), with both calling for his release.

US President Barack Obama said the US "stood in solidarity" with a number of detained activists, mentioning Tohti by name alongside imprisoned Chinese Nobel Prize winner Liu Xiaobo.

"They deserve to be free. They ought to be released," he said. "This growing crackdown on civil society is a campaign to undermine the very idea of democracy."

Separately, the White House urged Chinese authorities to differentiate between "peaceful dissent and violent extremism".

"We believe that civil society leaders like Ilham Tohti play a vital role in reducing the sources of inter-ethnic tension in China, and should not be persecuted for peacefully expressing their views," a statement said.

And Secretary of State John Kerry said the US was "deeply disturbed" by the life sentence, describing Tohti as "an important moderate Uighur voice".

The EU called the sentence "completely unjustified" and urged his immediate and unconditional release, echoing separate statements from countries including Britain and Germany.

China's foreign ministry hit back at the criticism.

"Certain countries hold high the banner of democracy and human rights and make irresponsible remarks," spokeswoman Hua Chunying told a regular briefing. "This is a groundless violation of China's internal affairs."

- Cultural and religious oppression -

Analysts were puzzled by the sentence, saying none of Tohti's writings or comments advocated a Uighur breakaway from China.

Xinjiang has been hit by a string of attacks on civilians and clashes which have killed at least 200 people in the last year.

"I think most observers of Xinjiang and Uighur issues will be very disheartened by this as it seems likely to add fuel to the fire of conflict in Xinjiang," Michael Clarke, an authority on Xinjiang at the Griffith Asia Institute in Australia, told AFP.

The resource-rich region is home to about 10 million Uighurs.

China blames the violence on "terrorist" groups seeking independence for the region, while rights groups say cultural and religious oppression of Uighurs has fuelled resentment.

The attacks have grown in scale and sophistication and have spread outside the region.

Police detained Tohti, who taught at a university in Beijing, in January after he criticised the government's response to a suicide car attack last October in Beijing's Tiananmen Square, which the government blamed on Xinjiang separatists.

Prosecutors at Tohti's trial presented videos of his university lectures and posts from his website Uighur Online as evidence that he had led a separatist group, Li said.

They also cited testimony from some of Tohti's students, around eight of whom have been detained.

AFP found no evidence of separatist remarks on an archive of the website, now closed.

- 'Calling out for my people' -

Barry Sautman, an expert on ethnic politics in China at Hong Kong University of Science and Technology, said Uighur intellectuals would be "really disappointed" by the sentence.

"They will have to wonder why he got such a harsh sentence compared to even the most prominent of Han intellectuals who is now sitting in prison for opposing the Chinese government, and that is Liu Xiaobo, who got 11 years," he said.

Liu was sentenced in 2009 after spearheading a bold petition for democratic reforms.

"Some people will of course draw the conclusion that if you are an ethnic minority person, particularly a Uighur, you are bound to get a harsher sentence than if you are not," Sautman added.

Li said Tohti told him that even though he is in prison, "I still look forward to the future and look forward to the sun".

"I am calling out for my people, and even more for the people of China," Tohti said, according to Li. "I believe this country will get better, and the interests of Uighurs can be respected."