Authorities have detained four people for questioning following a half dozen anti-terror raids in Brussels as part of an investigation that was not link to past extremist attacks in Paris and Brussels.

The federal prosecutor’s office said that “various weapons were found” in one of the raids.

At the same time, on the outskirts of Lille in northern France, 100 kilometers (62 miles) from Brussels, another major anti-terror operation was held, French media reported. The La Voix du Nord newspaper said one man was detained.

Belgium and France are both on high alert since extremist attacks have hit Paris and Brussels over the past few years.

Belgian media said the raids centered on a bikers group, the Kamikaze Riders, two of whom have been sentenced on anti-terror charges last year.

(AP)