Security forces raided a string of properties and 152 lock-up garages on Friday night and in the early hours of Saturday, Belgium’s federal prosecutor in Brussels said in an e-mailed statement. Prime Minister Charles Michel called a meeting of the National Security Council for noon in Brussels, his spokesman said.

On the 12 people arrested, “the investigating judge will decide on their possible detention later today,” the prosecutor said. He didn’t confirm a report by broadcaster VTM that the terrorists were planning to attack fans — possibly on Saturday — while Belgium’s soccer team play in the Euro 2016 tournament.

Counter-terrorism forces across Europe have increased security during the European soccer championships, particularly in France where the tournament is taking place until July 10. Belgium play Ireland in the southern French city of Bordeaux at 3 p.m.

In total, police questioned 40 people during Friday’s overnight raids. No arms or explosives were found, the prosecutor said.