Brussels remained on high alert Monday with increased security after a weekend sweep that left three in jail facing terrorism charges, including relatives of two of the March 22 suicide attackers.

The MIVB metro system said a half-dozen subway stations have reduced entry on request from authorities, but all subway lines in the Belgian capital were running during the morning rush hour.

On Saturday, authorities charged three men with terror-related crimes after raids and the detention of 40 people in a major investigation. Authorities said the probe required “immediate intervention” because they feared a new attack was close.

Among those arrested were relatives of the El-Bakraoui brothers, who were among the suicide bombers in the March 22 attacks.

“We know that radicalism, violent extremism, is in a small minority of the Muslim community and it targets families,” Interior Minister Jan Jambon said in an interview with RTBF radio, responding to a question about the family ties among those arrested. He declined to elaborate, beyond saying that “it makes it easier to follow them, because we know where the links are.”

Prime Minister Charles Michel said the nation would remain “extremely vigilant, hour by hour,” and that the terror level across the country would remain at the second-highest level, meaning a threat of an attack “is possible and likely.”

(AP)