Chinese authorities put a prominent scholar from the mostly-Muslim Uighur minority on trial for separatism Wednesday as critics warned the prosecution will worsen tensions in violence-wracked Xinjiang.

Ilham Tohti, a former economics professor at a university in Beijing, denied the charges -- which carry a life sentence -- at a court in the regional capital Urumqi.

"We don't see anything in the evidence presented which constitutes separatism," Li Fangping, Tohti's lawyer, told reporters outside the heavily-guarded courthouse. "He was just a scholar expressing his views."

Guzaili Nuer, Tohti's wife, was accompanied by several of his brothers and appeared distraught.

"He has never opposed the country or any ethnic group," she said. "He has never done anything like that."

She added that her husband, 44, had denied the charges but remained calm during the hearing.

The Uighur homeland Xinjiang has seen escalating violence between locals and security forces in the past year, with hundreds dead, and Beijing has launched a crackdown on "separatists" and "terrorists".

But the United States, European Union, and several human rights groups have called for the release of Tohti, an outspoken critic of China's policies towards Uighurs in the far western region.

"Ilham Tohti worked peacefully within Chinese laws, and we believe he should be released," Raphael Droszewski, first secretary for political affairs at the EU mission in China, told reporters in Urumqi as the trial was set to begin.

He was among nine diplomats from countries including Germany, Britain and Canada who had travelled to Urumqi to observe the proceedings but were barred from entering the court.

Several dozen police officers, some in plain clothes and others clad in riot gear, were standing guard outside the building and had blocked off the surrounding streets.

Calls to the Intermediate People's Court by AFP went unanswered.

Tohti was detained in January after he condemned the government's response to a suicide car attack in Beijing's Tiananmen Square which the government blamed on separatists from Xinjiang.

His prosecution -- almost certain to result in a guilty verdict -- risks silencing moderate Uighur voices and cutting off the possibility of dialogue, critics say.

Prosecutors cited posts on Tohti's website Uighur Online and the contents of his lectures at the Minzu University in Beijing to accuse him of leading a separatist group, according to his attorney Li.

- 'They follow me everywhere' -

In interviews, Tohti has stated his opposition to independence or separatism.

"Tohti has consistently, courageously, and unambiguously advocated peacefully for greater understanding and dialogue between various communities, and with the state," said Sophie Richardson, China director for US-based campaign group Human Rights Watch.

"If this is Beijing's definition of 'separatist' activities, it's hard to see tensions in Xinjiang and between the communities decreasing."

Alim Seytoff, president of the Uyghur American Association, said that by punishing Tohti, Beijing would "burn the bridge of peaceful reconciliation... and further increase the political tension" in the region.

"Ilham Tohti is exactly the kind of Uighur Chinese officials should look to in order to find peaceful and lasting solutions for the future," he added.

Separatism charges can carry the death penalty in China, but the wording of the indictment means life imprisonment is the heaviest sentence Tohti can face, said his lawyers.

Chinese courts are tightly controlled by the ruling Communist party and have a near-100 percent conviction rate in criminal cases.

Tohti devoted decades to researching government policy towards Uighurs, about 10 million of whom live in Xinjiang, a vast, resource-rich and strategically important region which abuts central Asia.

China blames ongoing unrest in the region on organised terrorists, while rights groups say cultural and religious repression of Uighurs has stoked violence.

As a professor and writer, Tohti was known for his moderate stance on Uighur issues but was repeatedly subject to house arrest and prevented from leaving the country.

He has been denied food and kept in shackles during his detention, his lawyers say, and before the trial his wife told AFP she is continually tailed by security agents.

"They follow me everywhere," Nuer said. "I'm worried about (Tohti's) health, he has heart and stomach troubles, and he hasn't been allowed to visit a hospital," she added.

In a 2011 essay, Tohti wrote: "I earnestly hope that my homeland can become as prosperous and developed as the rest of China. I worry about my homeland and my country falling into chaos and division."