Dozens of Belgian police, including armed special commandos, surrounded houses in a residential street in the district of Molenbeek on Monday, and the public broadcaster denied a report a man wanted in connection with the Paris attacks was arrested.
State-controlled RTBF carried a denial of a report by private broadcaster RTL that Saleh Abdeslam, a 26-year-old Frenchman based in the Belgian capital, had been detained.
Police said the operation was related to the Paris attacks.
Reuters journalists at the scene in Molenbeek said there had been little movement around police lines. Armoured vehicles remained in position.
The poor district of Molenbeek, home to many Muslim immigrants, has been at the centre of investigations of militant attacks in Paris over the weekend, after it emerged that two of the attackers had lived in the area.