A court in the Xinjiang region of north-west China sentenced the country’s most prominent peaceful advocate for the rights of Muslim Uighur people to life in prison for inciting separatism on Tuesday.

Ilham Tohti, a former economics professor at Minzu University of China in Beijing, is known as a moderate Uighur intellectual and critic of the government’s ethnic policies. He advocates increased autonomy and equal rights for Xinjiang’s minority groups. The 44-year-old has firmly denied the charge.

The US and EU have called for his release, and human rights groups have described the case as a political prosecution intended to showcase the government’s unwillingness to tolerate even moderate forms of dissent.

“Ilham’s case is an example of someone being convicted for speaking freely,” Tohti’s lawyer, Li Fangping, said by phone, adding that the defence would appeal against the verdict.

The court in Urumqi, the region’s capital, also demanded the seizure of all Tohti’s assets.

Xinjiang, a sparsely populated but ethnically diverse region, is more than six times the size of the UK and borders several central Asian states. Tensions between the region’s Muslim Uighur minority and majority Han Chinese have flared into clashes and terror attacks over the past year and a half. More than 200 people have died in Xinjiang-related violence since last spring. On Sunday, three explosions in the south of the region killed two people and injured many others.

China blames the conflict on independence-seeking separatists, terrorists, and the spread of radical Islam. Uighur groups abroad say the clashes are a desperate protest against religious oppression and economic marginalisation.

“Today, Ilham Tohti becomes another casualty of China’s war on words,” said Dominic Moran, the director of free expression programmes at the New York-based Pen American Centre. “His conviction makes a mockery of China’s professed commitment to social harmony by silencing one of the country’s unifying voices and, with it, fellow Uighur writers who are now unlikely to dare speak out.”

He added: “Pen upholds Tohti’s innocence, decries the profound iniquity of this judgment, and holds profound concerns regarding his maltreatment in detention. We maintain hope that, with time, justice will prevail and he will be freed to return to his wife and children.”

Xinhua, China’s official newswire, said afternoon that Tohti “spread lessons containing separatist thoughts via the website [Uighur] Online”.

Tohti launched the site in 2006 to provide an open, bilingual forum for Uighurs and Han Chinese to discuss the country’s ethnic issues. Authorities blocked the site two years later.

“He bewitched and coerced young ethnic students to work for the website and built a criminal syndicate,” Xinhua said, citing the court’s verdict. “Tohti organised this group to write, edit, translate and reprint articles seeking Xinjiang’s separation from China. Through online instigation, Tohti encouraged his fellow Uighurs to use violence. He also colluded with foreign groups and individuals in hyping incidents related to Xinjiang with the aim of making domestic issues international.”

According to Tohti’s lawyers, the academic has been kept in shackles and intermittently denied food and warm clothing during his detention.

Tohti was arrested in January and charged with separatism in June. Seven of his former students are also currently in detention, but their legal status remains unclear.

Maya Wang, a Hong Kong-based researcher for Human Rights Watch, called the sentence the harshest handed down to a peaceful government critic in recent history. The verdict is “a sign of further tightening of civil liberties that has been going on in the past year and a half – and it means that things might get worse in the future,” she said. “It certainly doesn’t bode well for the already tense relationship between Han and Uighurs in Xinjiang.”

Wang Lixiong, a prominent writer and activist in Beijing, tweeted: “On September 23, 2014, the Chinese authorities created the Uighur Nelson Mandela.”