Manfred Nowak, the U.N. Special Rapporteur on Torture, said his team was under frequent surveillance during a two-week trip that included Tibet and the northwestern Muslim-majority region of Xinjiang -- the first visit granted his office in a decade.

There was also evidence authorities had intimidated victims and family members the U.N. team tried to interview, he said.

"My preliminary conclusion is that as far as the amount of torture, I would recognise a certain decline ... but nevertheless torture remains widespread in the country," he told a news conference.

"Criminal procedures need to come into line with international standards of fair trial," he said.

Beijing has been grappling with a series of cases in which people have been wrongly convicted after giving forced confessions, a practice rights groups say happens too often.

China's parliament passed a bill earlier this year mandating punishment for police who torture detainees during interrogation.

In April, it freed a man who spent 11 years in jail for allegedly murdering his wife after the woman turned up alive. The man, She Xianglin, said he had confessed the crime under torture.

China's foreign ministry had said it was paying great attention to the visit, and it could be successful with hard work by both sides.

In a statement, Nowak said a number of family members and victims the team tried to visit were "intimidated by security personnel, placed under police surveillance, were told not to meet the special rapporteur, or were physically prevented from meeting with him".

"I observed a palpable level of fear and self-censorship of those detainees I interviewed," he said.

China is home to the world's biggest prison population and has a legal system the U.S. State Department says is characterised by mistreatment of prisoners and an "egregious" lack of due process in the use of the death penalty.

China signed the International Covenant of Civil and Political Rights in 1998 but has yet to ratify the treaty seen as a cornerstone of global rights law.

Source: Swissinfo