Yu Jie says house arrests and torture became part of everyday life after his friend Liu Xiaobo won the Nobel peace prize

A Chinese dissident author has accused state security officials of hoodingand stripping him, beating him unconscious and threatening to post naked pictures of him online. Yu Jie and his family left China for the US last week, blaming harassment by the authorities.

One of the government's most outspoken critics, Yu is best known for his book Wen Jiabao: China's Greatest Actor, but also angered authorities by writing an as-yet-unfinished biography of his friend Liu Xiaobo, the jailed Nobel peace prize winner.

In a lengthy statement, the 38-year-old said government censorship had made him "a non-existent person in the public space", unable to publish any work on the mainland. But his problems escalated when Liu's award was announced in October 2010 and "illegal house arrests, torture, surveillance, tracking, and being taken on 'trips' became part of my everyday life".

His family was placed under house arrest and even their phone and internet connections were cut, leaving them in "an endless black hole". The day before the Nobel ceremony in December, plain clothes officers hooded and abducted him and began beating him in the head and face, he said.

"They stripped off all my clothes and pushed me, naked, to the ground, and kicked me maniacally. They also had a camera and were taking pictures as I was being beaten, saying with glee that they would post the naked photos online," Yu added.

"They forced me to kneel and slapped me over a hundred times in the face. They even forced me to slap myself … They also kicked me in the chest and then stood on me after I had fallen to the ground."

He said they had threatened to break his fingers and burn his face with cigarettes, verbally abused him as "a traitor" and "trash" and insulted his friends and family, before forcing him to insult himself.

Yu said the head of the team told him: "Right now, foreigners are awarding Liu Xiaobo the Nobel peace prize, humiliating our party and government. We'll pound you to death to avenge this. As far as we … can tell, there are no more than 200 intellectuals in the country who oppose the Communist party and are influential. If the central authorities think that their rule is facing a crisis, they can capture them all in one night and bury them alive."

Officers took him to a hospital after he passed out from the abuse, Yu added. A senior officer later told him: "What happened yesterday was a misunderstanding – my subordinates' mistakes."

He finally decided to leave China because even after his release, his family was split up, his wife lost her job, and he was unable to regularly practise his faith as a Christian. But authorities warned him he would not be able to return home "if you say or do something you shouldn't".

Yu plans to finish his biography of Liu and write a book on Hu Jintao. He argued that while Jiang Zemin was president, there was "still a certain space for free speech", but that conditions deteriorated after Hu took power.

Last week, China's foreign ministry said it did not know of Yu's case. "China has too many people, and I don't know each of them," said a spokesman, Liu Weimin. "I don't know about this person."

The foreign ministry has also dismissed remarks this week by the US ambassador to Beijing, who said human rights had deteriorated in China since the Olympics in 2008. A spokesman described Gary Locke's remarks as "inconsistent with the facts".