The first minors convicted under Hong Kong’s national security law were sentenced to detention at a training center on Saturday by a judge who said their calls to overthrow the Chinese government must be met with deterrence.

A 16-year-old girl and three 17-year-olds were members of a little-known pro-independence group calling itself the Returning Valiant, which publicized a violent uprising against China at street stalls and on social media last year in court.

They were charged with “conspiracy to incite subversion” under a sweeping national security law Beijing imposed on the city to stamp out dissent after large and sometimes violent pro-democracy protests three years ago.

On Saturday, Judge Kwok Wai-kin said the defendants’ message could have turned peaceful protesters violent – although he conceded there was no direct evidence anyone was incited.

“Even if one person is incited, Hong Kong’s stability and the safety of residents could have been greatly affected,” Kwok said.

The four teenagers, who AFP declined to name because of their age, pleaded guilty last month along with 19-year-old co-defendant Kwok Man-hei.

All five were sentenced to up to three years in a training center, a rehabilitation-focused detention facility that can be a sentencing option for juveniles aged 14 to 20.

In an earlier hearing, prosecutor Stella Lo said the group circulated its messages outside of busy train stations, held press conferences and held online broadcasts over a four-month period.

The defendants cited the French Revolution and Ukraine’s struggle for democratization over the past decade to support their cause, the court heard.

Flyers distributed by the group also quoted Mao Zedong of the Chinese Communist Party as saying that “revolution is not a dinner party” but “an act of violence by which one class overthrows another,” Lo added.

Some of the teenagers were still at school when they were arrested.

The case also involves two adult defendants, whose sentences will be decided separately next month.

Most have already spent a year in pre-trial detention after new Security Law rules made it harder for suspects to bail.

The national security law states that anyone who incites subversion should be sentenced to between five and 10 years in prison if the case is serious.

Hong Kong courts typically refrain from sending minors to jail, preferring options that emphasize rehabilitation.

However, prosecutor Anthony Chau said sentences under the National Security Act must have a deterrent effect.

Defense attorneys argued that the door should be left open for the defendants to receive lighter sentences, given the typical discount of pleading guilty.

Hong Kong’s once-popular pro-democracy movement has been crushed by both the security law and prosecutors using a colonial-era sedition law.

More than 210 people have been arrested on the basis of the law, and nearly 130 have been formally charged, mostly for political views and speeches.

Authorities have launched a separate terrorism prosecution against other Returning Valiant members over an alleged bomb plot, with police accusing them of attempting to create the powerful explosive TATP.