The outgoing US ambassador to China urged Beijing on Thursday to respect the rights of peaceful political activists. He said that Washington was deeply concerned about the fate of minority scholar Ilham Tohti, who has been charged with separatism.

Tohti is an economics professor and outspoken advocate for the Uighur Muslim minority. He was arrested on Tuesday after being taken from his home a month ago.

At his final news conference as ambassador, Gary Locke also highlighted a recent increase in the arrests of social and legal activists and journalists.

According to Locke, China should value not just the economic welfare of its people, but also their freedom of speech, assembly and religion.

"We believe that freedom of expression is a universal right and we very much are concerned about the arrest and detentions of people who are engaged in peaceful advocacy", Locke said.

China's communist government brooks no political opposition and routinely rejects such remarks. Beijing says it must take harsh measures against what it calls Islamic terrorists fighting for the independence of Xinjiang, the Uighurs' homeland in north-western China. Violent incidents have increased over the past year.

Foreign ministry spokeswoman Hua Chunying defended China's record at a regular briefing on Wednesday and accused the country's critics of political bias.

Chinese citizens enjoy "unprecedented rights and liberty", Hua said. "We strongly oppose irresponsible comments made by anybody, regardless of which country he comes from."

A former commerce secretary and two-term governor of Washington state, Locke, 63, oversaw the defusing of two of the most delicate diplomatic episodes between China and the US in recent years.

In February 2012, Wang Lijun, the police chief in the western city of Chongqing, fled to a US consulate in south-west China with information about the killing of a British businessman, setting off a major political scandal. Wang's flight led to the removal and subsequent sentencing to life imprisonment for corruption of Chongqing's leader, Bo Xilai, formerly one of China's most powerful politicians.

Just two months later, the blind legal activist Chen Guangcheng escaped house arrest and was given shelter in the US embassy in Beijing, where he remained for six days before being allowed to leave the country with his family to study in New York.

In his comments, Locke also repeated Washington's calls for restraint in China's maritime territorial disputes with Japan and its south-east Asian neighbours. He urged China to accord foreign journalists working in the country the same equitable treatment Chinese journalists receive in the west, a reference to Beijing's denial of visas to reporters from the New York Times and other news outlets.

He did not refer to Chinese investment barriers, alleged currency manipulation and other economic disputes that had been prominent themes in Locke's speeches earlier in his term. This appeared to reflect a strengthening US economy and a boom in exports to China that are growing at nearly twice the rate they are to other countries. He said Chinese investment in the US over the past two years exceeded that of the previous 11 years.