Hong Kong police have signaled their intent to enforce a new Chinese national security law strictly, arresting four youths Wednesday on suspicion of inciting secession through social media posts. Three males and one female, aged 16 to 21, were detained, a police official said at an 11 p.m. news conference. All are believed to be students. “Our investigation showed that a group has recently announced on social media that they have set up an organization for Hong Kong independence," said Li Kwai-wah, senior superintendent of a newly formed unit to enforce the security law. The 1-month-old law has chilled pro-democracy protesting as activists along with academics and others wonder if their activities could be targeted. The central government in Beijing imposed the national security law on the semi-autonomous Chinese territory after city leaders were unable to get one passed locally. The move has raised fears that Hong Kongs freedoms and local autonomy are being taken away. Police did not identify the suspects or their group. An organization called Studentlocalism — which announced it was disbanding just before the law took effect — said on Facebook that four former members had been arrested on secession charges, including ex-leader Tony Chung. The police action appeared to target the Initiative Independence Party, which says on its Facebook page that it consists of former Studentlocalism members who have completed their studies and are overseas. The party, which also posted the news of Wednesdays arrests, advocates for independence because it believes full democracy for Hong Kong is impossible under Chinese rule, its Facebook page says. Li said only that the group in question had set up recently and that the posts were made after the law took effect late on June 30.