A Chinese court on Friday rejected an appeal against a life sentence handed to a prominent scholar from the mostly-Muslim Uighur minority, as a 70-year-old journalist stood trial in a deepening crackdown on dissent.

Rights groups have decried both cases as an effort to silence critics of the ruling Communist Party, which in recent years has stepped up a campaign against activists, lawyers, academics and journalists who fail to toe the party line.

Ilham Tohti, 45, had been an outspoken critic of China's policies towards the Uighur minority in their homeland of Xinjiang, which has been hit by a wave of violence which the government blames on separatist groups.

Rights groups say discrimination and government repression of the Uighurs' religion and language has fuelled violence, which has claimed more than 200 lives in the past year.

Tohti's life sentence in September was one of the harshest verdicts handed down to a government critic in decades, prompting an outcry from human rights groups as well as the US and European Union.

Tohti's lawyer Liu Xiaoyuan told AFP that authorities in Xinjiang's capital Urumqi rejected his appeal, and that the scholar -- who has been kept in leg-irons for months -- had pronounced the verdict "unjust".

"He maintains that his behaviour has not endangered state security," Liu said. "He is upholding his point of view. Anti-violence and anti-separatism have been his beliefs all along."

China's case against Tohti was in part based on recordings of university lectures in which he said that Xinjiang "firstly belonged to the Uighur ethnic group," rather than China's Han majority, state-run media reported.

Since coming to power in 2012, China's President Xi Jinping has overseen a campaign against government critics with hundreds detained or jailed.

They include prominent legal expert Xu Zhiyong, who was jailed for four years in January, and celebrated human rights lawyer Pu Zhiqiang, who was detained in May and has not been released.

- Crackdown on dissent -

Rejection of Tohti's appeal came as former reporter Gao Yu stood trial in Beijing where she denied charges of "leaking state secrets," in a case rights groups described as an attack on freedom of expression.

Gao, 70, went missing in April and was paraded on state-television a month later admitting she had made a "mistake," in a statement her lawyers say was made under duress.

The journalist -- who suffers from heart problems and paused several times to take medicine during the four-hour hearing -- told the court that "because of threats against my son, I confessed against my will," her lawyer Mo Shaoping told AFP.

Gao's attorneys argued that the prosecution's evidence was not sufficient to convict, Mo said, adding police detained her son for the trial's duration.

A well-known journalist who was named one of the International Press Institute's 50 "world press heroes" in 2000, Gao's political writings landed her in prison in the 1990s.

The current charges against her -- which carry a potential life sentence -- are reportedly in connection with the 2013 leaking of an internal Communist Party communique calling for a harsh crackdown on dissent and warning against such "perils" as Western-style democracy and criticism of the party's historical record.

- Case 'part of rule of law' -

Outside the Beijing No. 3 Intermediate People's Court, where Gao's trial is being conducted in secret, several dozen uniformed and plainclothes staff shoved reporters and prevented them from approaching the building.

"I'm from the hooligan department," one male plainclothes security officer said as he pushed an AFP reporter.

Asked about Tohti on Friday, Chinese foreign ministry spokesman Hong Lei told reporters that "dealing with the relevant case is a part of Chinese progress in the rule of law."

The United States said it was "deeply disappointed" by the decision to uphold Tohti's conviction and life sentence in a closed hearing.

"His detention silenced an important Uighur voice that peacefully promoted understanding among China's ethnic groups. We will continue to call for Chinese authorities to release professor Tohti," Jeff Rathke, a US State Department spokesman told reporters Friday.

The US was "deeply concerned" by Gao's trial and the detention of countless others who challenge Communist Party rule, Rathke said, urging China to "differentiate between peaceful dissent and violent extremism".

Sophie Richardson, China director for the US-based Human Rights Watch, called Gao's case "a frontal assault on the freedom of expression and access to information".

"State secrets laws have been a perfect weapon for prosecuting activists and whistleblowers like Gao Yu," she said.

William Nee, China researcher at British-based Amnesty International, said: "If Gao Yu and Ilham Tohti were to receive genuinely fair hearings, the charges against them would be dismissed as blatant political persecution."