Prominent Hong Kong pro-democracy activist Joshua Wong has been sentenced to 10 additional months in prison for taking part in an unauthorized assembly last year to commemorate the 1989 crackdown on pro-democracy demonstrators in Beijing’s Tiananmen Square.

The 24-year-old Wong is already serving a 13-and-a-half-month sentence for organizing an unauthorized protest in 2019. He was sentenced Thursday along with fellow activists Lester Shum, Jannelle Leung and Tiffany Yeun, who received sentences of between four and six months.

Wong was also among 47 activists charged under Hong Kong’s sweeping national security law for taking part in unofficial primary elections last July to pick candidates to run in legislative elections. They were then postponed due to the coronavirus pandemic.

China has banned any public observance of the June 4, 1989 crackdown, when Chinese military tanks and troops raided Tiananmen Square to break up weeks of student-led protests. But Hong Kong traditionally held large vigils to mark the event under its Basic Law, which granted the city certain freedoms not allowed on the mainland, including the right to assembly.

Last year's event was banned for the first time, with police citing the pandemic and security fears following huge and often violent pro-democracy protests that engulfed the financial hub in the last half of 2019.

Hong Kong authorities have increasingly clamped down on the city’s pro-democracy forces since Beijing imposed the new national security law last June in response to the 2019 demonstrations.

Under the law, anyone in Hong Kong believed to be carrying out terrorism, separatism, subversion of state power or collusion with foreign forces could be tried and face life in prison if convicted.