Belgian police detained six people during house searches over the New Year's attack plan in Brussels on Thursday.
Security forces launched operations at six locations in the Belgian capital and one of them was just outside the city, confiscating mobile phones, computers, and equipment for airsoft, a sport including guns that shoot non-lethal plastic pellets.
On Sunday and Monday, two Belgian citizens arrested and identified as 30-year-old Said S. and 27-year-old Mohammed K., are also being held for trial on suspicion of plotting a terrorist attack, prosecutors said. A court on Thursday extended their detention period for a month.
The two suspects are from the biker gang Kamikaze Riders, whose members are mostly from North African countries.
Two suicide bombers involved in the attack lived in Belgium, according to the French and Belgian authorities. A source close to the French investigation confirmed on Wednesday that more than one man was suspected of having coordinated the attacks by mobile phone from Belgium as they were being carried out.
Some Belgian media say the group sympathises DAESH terror organisation.
On Wednesday, Belgian authorities cancelled a traditional New Year's Eve fireworks display in the country’s capital to guard against a possible terror threat.
Brussels Mayor Yvan Mayeur told Radio Television Belge Francophone (RTBF) that "Together with the interior minister, we've decided to not have the celebrations on Thursday evening."
Attention has been focused on Belgium following the Paris attacks on November 13 that led to deaths of more than 130 people.
Since the deadly Paris attacks, Belgium has been on alert level three that means a potential serious threat. And last month, only Brussels was on the maximum alert level for a four week.
Federal prosecutors said on Thursday that a 10th suspect had been charged as part of the Paris attacks following 10 mobile phones were seized during the raid at a Molenbeek residence on Wednesday.