The three teenagers, suspected of having been in contact with four men arrested in Belgium on Sunday for a planned attack in Brussels, were indicted in France.
Two of them, aged 15 and 17, were placed in pre-trial detention.
The third, aged 15, is under judicial control, said the Pnat (national anti-terrorism prosecutor's office) this Friday.
On Monday, these minors were arrested in three cities in France by investigators from the General Directorate of Internal Security (DGSI).
They are not accused of being directly involved in the foiled attack plan, which targeted a concert hall in the Belgian capital, but of having adhered to Islamist theories, a source close to the matter clarified at the start of the week.
The teenagers “interacted in a group on a social network in which exchanges of jihadist propaganda took place and plans for an attack were mentioned,” Pnat explained on Tuesday.
“In this context, they were able to be in contact with other people, including certain individuals arrested in Belgium,” he added.
Two separate procedures
Their police custody took place within the framework of two separate procedures.
The first, which concerns a 15-year-old minor, has focused since November 2023 on a “terrorist criminal association (for wanting to join the Islamic State in the Iraqi-Syrian zone and planning to commit an attack) and apology for terrorism (for dissemination propaganda of the Islamic State)”.
The latter was placed in pre-trial detention.
Another 15-year-old minor has been indicted for these facts since November 2023.
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The second was opened last week for “terrorist criminal association with a view to preparing one or more crimes of personal injury”.
The two other adolescents were indicted as part of these investigations.
The 15-year-old was placed under judicial supervision and the 17-year-old was incarcerated.
On Sunday, Belgian police arrested four men - "three minors in their late teens" and an 18-year-old young man - during searches carried out in Brussels, Ninove, Charleroi and Liège, according to the spokesperson for the Belgian federal prosecutor's office Éric Van Der Sypt.
They were suspected of “planning a terrorist attack in Belgium”.
According to RTBF, these arrests resulted from a police operation aimed at identifying people “potentially violent and suspected of being linked to Islamist extremism”.
No weapons or explosives were found.
But the messages exchanged by the four suspects were “sufficiently worrying for us to intervene and carry out searches,” declared Éric Van Der Sypt.
“It's not that they were planning something for tomorrow, but it was imminent enough to intervene,” he continued.
The relative youth of the suspects reinforced the authorities' distrust.
“They are very flexible.
If someone gives them a gun, for example, things can happen very, very quickly.
We therefore do not want to take any risks,” the spokesperson said.