Brussels Square
Brussels SquareiStock

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, according to The Associated Press.

Those arrested include an adult who has been charged with "participation in the activities of a terrorist group” with the aim of committing an attack, as well as three underage individuals.

"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.

The terrorist threat level in Belgium was raised from two to three in October, the second-highest level and considered "serious".

This followed an attack in the Belgian capital in which two Swedish nationals were shot dead, and another injured, by a radicalized Tunisian.

The attacker was shot dead by Belgian police on October 17, the day after the attack.

Weeks after that attack, a Palestinian Arab asylum seeker was arrested in Brussels after he visited a migrant aid organization where he allegedly talked about planning a suicide attack.

Brussels was hit with a major terrorist attack in 2016, in which 32 people were murdered by Islamists.

Reports following the 2016 bombing indicated that Belgium received advanced warnings of the terrorist attacks but did not act on those warnings.

A jury last year found six people guilty of terrorist murder for the 2016 attacks. 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 2015 attacks in Paris that were claimed by the Islamic State (ISIS).