BRUSSELS -- Belgian authorities have detained 12 people for interrogation following raids linked to last year's Brussels attacks.

Police raided 14 places in and around Brussels on Tuesday and an investigating judge will decide later whether any of the detainees will be charged.

The federal prosecutor's office refused to elaborate beyond a terse statement.

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On March 22 last year, 32 people were killed in twin attacks on the Brussels airport and the subway system. Belgium is still in a heightened state of security.

Belgian leaders, victims and families of those who died in the suicide bomb attacks on the Brussels airport and subway marked the first anniversary of the assaults in March. King Philippe and Queen Mathilde joined Prime Minister Charles Michel at the airport, where two suicide bombers blew themselves up in the departure hall during the morning peak travel period on March 22, 2016.

Airport staff, security and rescue personnel stood watch as King Philippe laid a wreath outside the departure hall of the Belgian capital's Zaventem airport, where 16 people lost their lives. The names of those who died were read out solemnly, accompanied by a single cello.

Inside the departure hall, a large wreath lay in a cordoned-off area.

More than 300 people were wounded in the attacks, claimed by the Islamic State of Iraq and Syria (ISIS), but around 900 people now number themselves among the victims to have suffered physical or mental trauma.

CBS News' Holly Williams reported that the timing of the 2016 attacks may have been forced by the pressure Belgian police were putting on the terrorists. Days before the assaults, they raided a Brussels apartment and arrested one of the conspirators linked to the 2015 attacks in Paris that killed 130 people. On March 18 last year, Salah Abdeslam, 26, was captured after an intense four-month manhunt.