A Chinese judge has sentenced Ilham Tohti to life in prison, in a decision human rights advocates called a shockingly severe move to silence a prominent critic of the country's policies toward a Muslim minority.

On Tuesday, a court in Urumqi, the western capital of the Xinjiang territory that is home to China's Uyghur people, found Mr. Tohti guilty of separatism, seized his assets and revoked his political rights for life, which means he will no longer be entitled to free speech.

His sentence far exceeded the minimum 10 years his lawyers and family had hoped for and drew swift condemnation from the international community. Its seriousness is likely to serve as a significant new deterrent against those willing to speak out against a Chinese government that, under president Xi Jinping, has grown increasingly intolerant of dissent.

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Indeed, among the wrongdoings attributed to Mr. Tohti was "taking advantage of the international media to put pressure on China," his lawyer, Li Fangping, said in an interview.

When the sentence was read in court, Mr. Tohti's wife Guzailai Nu'er broke down weeping in court, Mr. Li said.

"She was barely able to stand in the end," he said. "Though we had somewhat prepared for such a harsh outcome, we still thought the broad concerns about the case might have produced a lighter punishment for him."

Mr. Tohti is an economist who worked as a professor at Beijing's Central University for Nationalities before being arrested in January. Uyghur by ethnicity, Mr. Tohti was a prominent voice in defence of what he considered mistreatment of his people by Chinese authorities.

The Uyghurs are a largely-Muslim group who face restrictions on dress, religious practice and mobility amid an outbreak of terrorist attacks that Chinese authorities have blamed on separatist extremists in their midst. Though some Uyghurs have advocated independence, Mr. Tohti was a moderate who called for better relations with China. He was, however, unwilling to bend to mounting government pressure that he mute his condemnation of policies he publicly called wrong-headed.

After months of detention that saw him lose significant weight, he faced a two-day trial last week. Envoys from numerous countries, including Canada, sought but were refused entrance to the court. The U.S. has urged China to release Mr. Tohti, while the European Union on Tuesday called his sentence "completely unjustified."

"The EU deplores that the due process of law was not respected, in particular with regard to the right to a proper defence," the EU said in a statement.

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Mr. Tohti was not permitted to address the court at his sentencing. But as he left the courtroom, he spoke in defiance: "I disagree with this sentence and I protest," he said, according to Mr. Li. The family intends to appeal the ruling. But the speed of the court verdict and the severity of the punishment made clear "the authorities' so-called determination to fight against those who would split the country," the lawyer said.

The lengthy sentence far exceeds that given other Chinese activists in recent years and won plaudits inside China, where the iron-fisted government campaign against terrorism has been popular. Yan Xuetong, dean of the Institute of Modern International Relations at Tsinghua University, offered a comparison to the muscular American actions following the Sept. 11 attacks. International media "is over-sensitive and over-reacting" to a Chinese response to separatism, which Mr. Yan acknowledged was political in nature. But, he said, "I doubt any country's government response toward separatists is not politically motivated," he said.

China's foreign ministry spokeswoman Hua Chunying on Tuesday said: "I would like to remind you that China is a country ruled by the law, and the Chinese judicial organs will deal with this case in accordance with the law."

A life sentence in China can, in some instances, mean imprisonment until death. But it can be reduced to as few as 10 years through good behaviour and public acknowledgment of wrongdoing.

Human rights advocates nonetheless expressed shock at Mr. Tohti's sentence, saying it marks a new degree of severity in China's response to critics. The past 18 months have seen a constriction in Chinese civil liberties that has further constrained online speech and led to dozens of human rights lawyers and other activists being tried and imprisoned, some as long as 13 years.

But a life sentence "is quite a bit harsher," said Maya Wang, a China researcher with Human Rights Watch. "It's a significant attack on China's civil society."

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Hu Jia, a prominent Chinese dissident, said it amounts to Beijing saying in some areas, it will broker no criticism.

"This is telling people that not only are you not allowed to do anything [to defy the state], you are also not allowed to say anything," he said. It is also a deliberate show of force by China to the international community, he said. Western nations implored China to go easy on Mr. Tohti. Beijing did the opposite, in effect saying, "we are not afraid of international pressure or concerns. Now is the time to show you our strength," Mr. Hu said.

Inside China, references to Mr. Tohti were heavily censored on domestic social media. Discussion of his case nevertheless managed to filter through amid a cloaked debate over the legitimacy of the case against him. Some sought proof of wrongdoing.

"Can the authorities show us his speeches and articles? If the state can be overthrown by one person's articles and speeches, it may be too fragile!" wrote one user on Weibo, China's answer to Twitter.

Another replied: "The country may not be overthrown by his articles and speeches. But let him keep going, and many people – including you – could be stabbed to death by the terrorists he incited."