Hong Kong officials stopped activists from sailing to the Diaoyu Islands last week out of concern that the Japanese navy might have sunk their ship, Chief Executive Donald Tsang Yam-kuen said yesterday. But his remarks in the Legislative Council were loudly dismissed by League of Social Democrats' lawmakers. 'You are also a Chinese. Why did you try to aid evil-doers at a time when the Chinese Communist Party was sucking up to the Japanese?' Leung Kwok-hung said. Early this month, the activists twice set out to declare Chinese sovereignty over the islands but were stopped by the Marine Department and police. It was the first time local authorities had blocked protest trips by the Action Committee for Defending the Diaoyu Islands. Activists and commentators linked the government's move to Beijing's unwillingness to jeopardise warming Sino-Japanese ties. Some also said the central government's liaison office had played a role. Mr Tsang said officials had a duty to ensure Hongkongers' safety, and pointed to an incident last June when the Japanese navy sank a vessel being used by Taiwanese activists trying to stake a claim to the islands. 'The director of the Marine Department ... must consider whether the present situation would have been similar to last year, and if the boat were rammed whether it would endanger those inside.' He said the vessel was licensed as a fishing boat but was not being used for that purpose. 'The boat ... was not solely used for fishing.' He also addressed Mr Leung's accusation that the government had failed to ensure the Tiananmen Square crackdown was being adequately covered in schools. 'I am very interested in this topic and I have looked at a few high-school textbooks. I found sections about June 4. They are very detailed and not simply one or two sentences.' His answers were attacked by league chairman Wong Yuk-man, who shouted: 'Traitor trying to sell out the nation!' Mr Leung added: 'When I go to defend the Diaoyu Island, you repeatedly send your cronies to stop us ... I was fighting against oppression, but you stopped the boat. Traitors are in power.'