HONG KONG (AP) — Hong Kong police on Tuesday arrested six people, including a former organizer of the city’s decades-long annual vigil that commemorated China’s Tiananmen Square crackdown, for allegedly publishing seditious social media posts, in what were the first publicly known arrests under the city’s new national security law.

Secretary for Security Chris Tang said Chow Hang-tung, a former leader of the group behind the vigil, alongside five others, used a social media page to anonymously publish the posts. Police said their acts began in April and that the suspects were targeting a “sensitive date."

The authorities have not detailed the content of the posts. But the page started publishing a series of posts to mark the upcoming 35th anniversary of the 1989 crackdown, a politically sensitive topic in Hong Kong and mainland China, on April 30.

“(They) provoke hatred against the central government, the Hong Kong government and the city's judicial institutions, and aim to incite netizens to organize or participate in illegal activities during a later period,” the police statement said.

The statement did not include other details on the social media page or the content of the posts, and it did not identify the six people, aged between 37 and 65, who were arrested.

The introduction of the new security law in March — four years after Beijing imposed a similar law that had all but wiped out public dissent — has deepened worries about the erosion of the city's freedoms.

The new law, known locally as “Article 23,” has expanded the government’s power to deal with future challenges to its rule, punishing treason and insurrection with up to life imprisonment.

Under the legislation, offenders who commit sedition offenses face harsher penalties than before. They face a maximum jail term of seven years if convicted for committing seditious acts or uttering seditious words — up from the previous maximum sentence of two years.

Authorities raided the homes of five of the suspects and seized items including electronic devices that officers suspect were used to publish the seditious messages, police said.

When Britain handed Hong Kong back to China in 1997, Beijing promised to retain the city’s Western-style liberties for 50 years. However, since the introduction of the 2020 law, Hong Kong authorities have severely limited free speech and assembly under the rubric of maintaining national security. Many activists were arrested, silenced or forced into self-exile.

The Beijing and Hong Kong governments say the China-imposed law helped return stability following huge anti-government protests in 2019.