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One of China's best-known dissidents, Chen Guangcheng, has escaped from house arrest and has released a video addressed to Premier Wen Jiabao.

In it he makes three demands, including one that Mr Wen investigate what Mr Chen, who is blind, calls the brutal beating up of his family members.

Rights activists say Mr Chen slipped out of his home in Dongshigu town in Shandong province on Sunday.

The US is refusing to comment on claims he is at the US embassy in Beijing.

Mr Chen, 40, had been under house arrest since he was released from a four-year jail sentence in 2010.

In the video, delivered from a darkened room, he said outwitting the guards keeping him under illegal house arrest had not been easy.

In the appeal, posted online by Boxun, a Chinese dissident news website based in the United States, he asks that:

Mr Chen names some local officials who told him that they "do not care about the law" and that "a few hundred people" were hired by the local government to "lock down" the village he lives in.

The Chinese authorities have come under international criticism for their treatment of him. At one point his daughter was barred from school. Many sympathisers who have tried to visit his home say they have been beaten up.

In the video, Mr Chen says: ''I may be free but my worries are for my family… my wife, my child, my mother. Perhaps because of my leaving, they may become the target of more brutal abuse.''

'Long-planned escape'

In an interview with the ����ý, another prominent activist Hu Jia said he had met Chen Guangcheng in the last 72 hours, since Mr Chen's escape.

He said Mr Chen had "planned this escape for a long time, he even attempted to dig a tunnel to escape.

"That failed and this time he tried not to appear in the day time to create the impression for the guards that he never appears in the day. So that won him time, a few days, to climb over all the walls. So he planned this for a long time and made sure the guards had no idea."

He said a night-time escape was not a problem for a blind man, but "of course he did fall a few times" - amid reports Mr Chen had to scale a high wall.

He said he had critical help from "volunteers".

Mr Hu say Mr Chen was driven hundreds of kilometres to the US embassy in Beijing.

The US embassy has not commented, and the US state department told reporters in Washington it had "no information" for them.

The plight of Mr Chen has become famous around the world. US Secretary of State Hillary Clinton has repeatedly called for his release and is due to visit Beijing next week.

The authorities appear to be moving against those believed to have been involved in Mr Chen's escape.

Reports on Friday said local authorities had surrounded the house of Mr Chen's brother, Chen Guangfu, and nephew, Chen Kegui, in Dongshigu, near Linyi.

Another activist based in China, He Peirong, who has been campaigning for Chen Guangcheng's freedom, told AP that Chen Kegui "took a cleaver for self-defence''.

''He said he hacked several people with the cleaver and wounded them," she said.

In the same report, Bob Fu, founder of US-based ChinaAid said Chen Guangfu and Chen Kegui had been detained by police.

He later told AFP news agency that Ms He had been arrested at her home in Nanjing on Friday.

Lost sight

Chen Guangcheng, who has been under house arrest for almost 20 months following his release after serving four years in jail, is known as ''the barefoot lawyer''.

He lost his sight in childhood. He has no formal legal training as the blind were not permitted to attend college.

He is known for revealing rights abuses under China's one-child policy and has accused officials in Shandong province of forcing 7,000 women into abortions or sterilisations.

He has also advised farmers in land disputes and campaigned for improved treatment of the disabled.

The Chen affair comes at an unwelcome time for China's leaders, who have been embroiled in a lurid political scandal involving disgraced former party boss Bo Xilai.

Mr Bo - a high flier once expected to reach the top echelons of office - has not been seen in public since he was removed from his political posts, in the biggest political shake-up in China in years.

Mr Bo's wife is being investigated over the death of British national Neil Heywood.