HONG KONG (AP) — The mastermind behind a foiled bomb plot during anti-government protests in Hong Kong in 2019 has been jailed for nearly 24 years in the city's first case brought under a United Nations anti-terrorism law.

Ng Chi-hung, who had previously pleaded guilty to conspiring to commit the bombing of prescribed objects under the anti-terror law and possession of arms or ammunition with intent to endanger life, was sentenced to 23 years and 10 months by a Hong Kong court on Thursday.

He was among seven convicted defendants who appeared in court for their roles in the plot to plant two bombs and shoot officers along a rally route on Dec. 8, 2019, during a time when accusations of police brutality in handling protesters were widespread.

The seven are not well-known activists in the semi-autonomous Chinese city’s pro-democracy movement, but their case has drawn attention because the United Nations (Anti-Terrorism Measures) Ordinance was invoked.

Hong Kong enacted the law to implement a U.N. Security Council resolution passed after the Sept. 11, 2001, attacks in the United States.

According to local media, prosecutors said most of the defendants in the case were members of two groups — one led by Ng and another called “Dragon Slaying Brigade." The prosecution said members of the brigade planned to lure police officers onto an area where bombs would be detonated and a sniper would target them.

Wong Chun-keung, leader of the brigade, was sentenced to more than 13 years. Five other defendants received prison terms ranging from nearly six years to 12 years.

In August, six other defendants, who had pleaded not guilty, were acquitted by a panel of jurors.

The 2019 protests marked the most concerted challenge to the Hong Kong government since the former British colony returned to Chinese rule in 1997.

Following the protests, more than 10,000 people have been arrested in connection with the often-violent social unrest sparked by a now-withdrawn extradition bill, which would have allowed suspects in Hong Kong to be sent to mainland China.