The raids have uncovered what is being described as “alarming” evidence of a Europe-wide jihadist cell connected to the attacks in Belgium as well as those in Paris in November.
Two brothers who died as suicide bombers in the attacks in Brussels last week were known to police as petty criminals and potential terrorists.
Ibrahim El Bakraoui, who blew himself up in the airport, had been arrested and deported from Turkey and labelled a “foreign terrorist fighter.”
His brother Khalid, who died in the subway attack, was subject to an international arrest warrant after the Paris attacks.
Officials have told CBS News that the brothers were on the radar of U.S. law enforcement.
DNA found on a suicide vest and a piece of cloth at the Bataclan concert hall massacre in Paris and a bomb at the Stade de France stadium was that of Brussels airport bomber Najim Laachraoui.