As authorities across Europe searched for Paris terror attack suspect Salah Abdeslam, Belgian authorities announced they had charged a fourth suspect Monday, the Associated Press reported. The name of the suspect was not revealed.

“The investigating judge specialized in terrorism cases placed into custody a man arrested during the operations of last night. He is charged with participating in activities of a terrorist group and with terrorist attack [Paris],” a statement from the prosecutor's office said, Agence France-Presse reported.

Belgium’s security forces continued to raid neighborhoods, including the Brussels district of Molenbeek, an area several of the suspects in the Paris attacks had ties with. The Islamic State group, aka ISIS, claimed responsibility for the Nov. 13 Paris attacks that left at least 130 people dead and over 350 injured.

The unnamed suspect charged Monday was arrested along with 15 other people in a raid Sunday evening. The other 15 people were later released, authorities said.

Mohammed Amri, 27, and Hamza Attou, 20, were charged last week with aiding Abdeslam, who reportedly fled to Brussels following the Paris attacks. The name of a third person charged in Belgium also has not yet been released. The third suspect was accused of helping Abdeslam after he entered the country.

Authorities in Belgium have warned of the possibility of a Paris-style attack in Brussels and have stepped up security in recent days. Brussels continued to remain on partial lockdown for the third day Monday, with vendors telling International Business Times that the city’s residents were heeding authorities’ calls to avoid busy areas. Subways and popular shopping areas as well as schools were closed Monday.

“It’s no good. We’ve never seen it this dead,” a flower vendor told IBT.

France has increased its airstrikes in Syria targeting ISIS, and British Prime Minister David Cameron said Monday he would seek approval from Parliament to join the assault. The U.S. and Russia have also been carrying out airstrikes in Syria.