Police in Belgium have arrested four people suspected of plotting an attack against a concert hall in Brussels, the federal prosecutor's office said Monday.

The adult arrested has been charged with "participation in the activities of a terrorist group" with the aim of committing an attack, the office said. Three underage individuals also were arrested.

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"According to the initial findings of (the) investigation, it appears that a Brussels concert hall was specifically targeted, with an attack planned in a few weeks’ time," the office said, without further details.

Belgium has been rocked by extremist attacks in recent years. The latest took place in October when two Swedish soccer fans were killed in Brussels.

A jury last year found six people guilty of terrorist murder for extremist attacks at the Brussels airport and a subway station that killed 32 people in Belgium’s deadliest peacetime violence in 2016, part of a wave of attacks in Europe linked to the Islamic State group.

Among those convicted for their role in the 2016 suicide bombing plot was Salah Abdeslam, who already is serving a life sentence without parole in France over his role in attacks that hit Paris cafes, the Bataclan music venue and France’s national stadium in 2015.

The Paris and Brussels attacks were linked to the same IS network.