Beijing police claim they have no record of detaining missing Aids activist Wan Yanhai, a colleague said yesterday. Hu Jia, who works with Mr Wan at Aids concern group Aizhi Action Project, filed a missing persons report with the Beijing Public Security Bureau last Wednesday. Mr Wan was last seen on August 24 at a cafe near the Workers Stadium. Earlier reports suggested Mr Wan had been under close surveillance by undercover police before his disappearance. Human rights groups have expressed concern that Mr Wan might have been detained over his use of the Internet to promote awareness of Aids. Mr Hu said he was hoping to find further clues about his friend's disappearance by visiting his apartment. He said he had not asked police to search the apartment because he feared it would compromise Mr Wan's work. Meanwhile, in Hong Kong about 20 human rights campaigners yesterday marched to the Beijing Liaison Office demanding that the Chinese government investigate the disappearance. However, Christine Or Yan-yan, project officer for the Justice and Peace Commission of the Hong Kong Catholic Diocese, said security guards at the Liaison Office shut the gate and threw away their petition after tearing it up. 'This has never happened before,' she said. 'The Liaison Office represents the Chinese government. How can they behave like that?' Ms Or said activists had contacted police in Beijing many times for information, but to no avail. 'We plan to ask for help from Hong Kong members of the National People's Congress.' Frank Lu Siqing, of the Hong Kong-based Information Centre for Human Rights and Democracy, said Beijing police had no reason to detain Mr Wan. 'This incident is completely unrelated to politics. He only expressed his concerns about Aids in China. He should not be detained,' Mr Lu said.