Six people were detained in connection with an attack last year on a Thalys express train to France that was foiled by three Americans, Belgian authorities said Monday.
The Federal Prosecutor’s Office said six houses in the greater Brussels area were searched in the operation and an investigating judge was to decide later whether the people taken in for questioning should remain in custody.
No arms or explosives were found and the prosecutor’s office said no further information would be made public about the people detained or the items seized in the police searches.
On August 21, 2015, a man on a Thalys train that had just crossed into France from Belgium tried to open fire with an assault rifle but was overpowered by three Americans, two of them off-duty members of the U.S. armed forces. French police termed it an Islamic extremist attack, but the alleged gunman, Ayoub El Khazzani, maintained he wanted to commit a robbery.
French authorities have linked El Khazzani to Abdelhamid Abaaoud, the ringleader of the Islamic State cell that attacked Paris in November and Brussels in March.
Brussels was on high alert Monday with increased security after another police sweep over the weekend that left three in jail facing terrorism charges, including relatives of two of the suicide bombers involved in the March attacks. Those bombings, at the Brussels airport and in the subway, killed 32 people. The November attacks at a club, cafes and a stadium in Paris killed 130.
The MIVB metro system in Brussels said a half-dozen subway stations had reduced entry by 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 March.
“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.”