Explosives, handmade belts, and the fingerprint of a Paris attacks fugitive were found in a Brussels apartment, prosecutors say.
The property in the district of Schaerbeek had been rented under a false name that might have been used by a person already in custody related to the Paris attacks, officials added.
The find suggests that the 13 November shooting and suicide bomb attacks in Paris, in which 130 people were killed, were at least partially planned in Belgium.
A fingerprint belonging to Paris attacks fugitive Salah Abdeslam was discovered, along with clues suggesting explosive belts may have been manufactured there.
"Material that can be used to fabricate explosives as well as traces of TATP (acetone peroxide) were found," a statement from the Belgian federal prosecutor said.
"Three handmade belts that might be used to transport explosives as well as a fingerprint of Salah Abdeslam were also discovered."
Acetone peroxide is an ingredient which is often used in improvised explosive devices used by terrorist groups.
It is relatively cheap and easy to obtain, around the world because of its low cost and relative ease to obtain.
Abdeslam's brother Brahim blew himself up during the Paris attacks. He is still on the run after disappearing following the massacres.
The attackers wore suicide vests during their attacks on the Stade de France, Bataclan, and bars and restaurants.