Prime Minister Charles Michel summoned security and intelligence chiefs for an emergency sitting of Belgium's national security council on Wednesday after an armed suspect was shot dead following a raid linked to the Paris attacks.
One Belgian private broadcaster, VTM, said two further suspects had been detained but there was no confirmation.
Brussels police killed the unidentified person who had an assault rifle after four officers were wounded on Tuesday during what investigators had expected to be a routine search on an apartment in the south of the Belgian capital.
Michel told RTL radio on Wednesday morning that police planned further operations in the coming hours and days.
Read also: A gunman killed 3 and injured 14 in America’s latest mass shooting
"The threat remains," Michel said, adding that Belgium would review its level of alertness and consider possible extra measures during the day.
Brussels, headquarters of the European Union as well as Western military alliance NATO, was entirely locked down for days shortly after the Nov. 13 Paris attacks for fear of a major incident there. Several of those involved in the Islamic State shootings and suicide bombings were based in the city.
Brussels has maintained a high state of security alert since then, with military patrols a regular sight.