Doug Stanglin

USA TODAY

After a series of overnight police raids netted a dozen arrests, Belgian authorities charged three people Saturday with terror-related crimes in an operation driven by fears of an imminent attack.

The three Belgian nationals were charged “as perpetrator or co-perpetrator, for having attempted to commit a terrorist murder and for participation in the activities of a terrorist group,” the federal prosecutor's office said in a statement. Nine people detained in the sweep late Friday and early Saturday were freed.

Public broadcaster RTBF said some of the suspects were reportedly seen driving by car in the center of Brussels around the Place Rogier where a giant screen was set up for fans to watch a broadcast of Saturday's Euro 2016 match between Belgium and the Republic of Ireland.

The prosecutor's office said the raids were mounted in 16 municipalities, many around Brussels, when their investigation "necessitated an immediate intervention," according to the Belgian newspaper Le Soir.

“It will be the case in the coming hours that we will take additional and adapted measures,” said Prime Minister Charles Michel after a meeting of the nation’s security council. He refused to elaborate on the nature of the threat.

“It is not over. We remain under terror alert 3, it means that something is still up,” Interior Minister Jan Jambon said, according to the Associated Press. “Last night, we had a very successful action.”

Among the municipalities where the raids took place were Molenbeek and Schaerbeek, two Brussels suburbs where suspected terrorists were detained in recent weeks following the March 22 suicide bombings at the Brussels airport and metro system that left 32 people dead.

Belgian media reports four federal ministers, including Michel and Justice Minister Koen Geens, and their families are under increased police protection.

“We learned about that late yesterday that this close protection would happen. They say there are good reasons for that,” Geens said.