HONG KONG, Aug 19 (Reuters) - Four Hong Kong student leaders charged with "advocating terrorism" after their union passed a motion last month mourning the death of a 50-year-old who stabbed a policeman before killing himself were denied bail on Thursday. The four, aged 18-20 and all from the University of Hong Kong (HKU), are the latest democracy activists to be denied bail under a sweeping national security law that Beijing imposed on the former British colony last year. Some student supporters burst into tears as they left West Kowloon Court where Kinson Cheung King-sang, 19, Kwok Wing-ho, 20, Chris Shing-hang Todorovski, 18, and Yung Chung-hei, 19, were denied bail. Magistrate Peter Law initially granted bail to Yung but the decision was immediately appealed by the prosecutors. The case was adjourned to Sept. 14. "I didn’t expect university students to be charged with advocating terrorism. They just issued a statement," said Jeff, 18, a student at HKU outside the court. An officer was stabbed from behind on July 1, while on duty with other policemen preventing demonstrations on the anniversary of the city"s return to Chinese rule in 1997. The man then stabbed himself in the chest and died in hospital. The policeman, 28, suffered a punctured lung, but survived what Secretary for Security Chris Tang described as a terrorist act by a "lone wolf". Shortly after the attack, a few dozen members of the HKU student union passed a motion, since withdrawn, to commemorate the 50-year-old"s death and appreciate his "sacrifice". Leaders of the union later apologised, retracted the motion and resigned from their posts. The union"s campus office has since been raided by national security police and the university has severed ties with the union and banned about 30 students who signed the motion from entering its premises. During anti-government protests that roiled the city in 2019, authorities described student campuses, where some of the fiercest fighting erupted, as being hotbeds of violence. Reporting by Jessie Pang; Editing by Anne Marie Roantree and Nick Macfie Our Standards: The Thomson Reuters Trust Principles.