Belgium officials said an ISIS flag and a Jihadist manual were found beside a man shot dead by police during a raid on a Brussels flat.
They said the man was an Algerian and in Belgium illegally.
Police operations are continuing in Belgium as investigators hunt for possible accomplices of the gunman killed in a raid linked to the November 13 attacks in Paris.
Three Belgian and one French officer were hurt in the operation on Tuesday, after authorities said investigators came under fire and stormed a house in Brussels, killing a suspect armed with an assault rifle.
Authorities were trying to determine if other suspects remain in the capital.
The anti-terror raid in the Forest neighbourhood of the city was linked to the November gun and suicide bomb attacks on a stadium, cafes and a concert hall in Paris in which 130 people were killed.
Belgian nationals played key roles in the attack.