Brussels: The Belgian police released without charges six people who had been held for questioning on Monday over an attack on a high-speed train as it travelled between Amsterdam and Paris in August 2015, prosecutors said.
In that attack, a man with a machine gun wounded two people on the train before being overpowered by passengers.
The new detentions follow a series of police raids on homes over the weekend, after which three men were charged with plotting an attack.
Prosecutors said that a judge had ordered six home searches and detained six people in the greater Brussels area. No weapons or explosives were found.
"They were released as planned after some checks," a spokesman for the Belgian federal prosecutor said. "There were no charges, either."
Belgium remains on heightened alert three months after three suicide bombers killed 32 victims in attacks on Brussels airport and a metro car.
Belgian media reported the men arrested at the weekend had planned to attacks fans watching the Euro 2016 games in Brussels.