Belgian police arrested 12 people suspected of planning new attacks after about 40 houses were searched across the country overnight, says the federal prosecutor's office.
Europe is on high security alert, with the Euro 2016 soccer tournament under way in neighbouring France.
"In connection with a criminal investigation concerning terrorism... 40 persons were taken for questioning. Twelve among them were arrested. The investigating judge will decide on their possible detention later today," the office said in a statement.
Investigators have found links between the Brussels and Paris attackers, some of whom were based in Belgium.
Belgium's federal prosecutor's office said no weapons or explosives were found during the searches, which also involved 152 garage lock-ups.
A French police couple were stabbed to death outside their home on Tuesday in an attack claimed by Islamic State.
In a video posted on social networks, the attacker linked it to the soccer tournament, saying: "The Euros will be a graveyard."
Flemish public broadcaster VTM said the people arrested overnight were suspected of planning an attack in Brussels this weekend during one of Belgium's soccer matches.
Belgian police on Wednesday received an anti-terror alert warning that a group of Islamic State fighters recently left Syria en route for Europe planning attacks in Belgium and France, security officials said.
Belgian newspaper Le Soir said areas where fans watch matches were potential targets, as well as other crowded areas like shopping centres and stations, citing a security source.
Public broadcaster RTBF said the country's crisis centre on Friday placed several government ministers, including Prime Minister Charles Michel, under heightened protection.
Police arrested and detained a man named as Youssef E.A, a Belgian national, on Friday on suspicion of taking part in terrorist activities in connection with the Brussels attacks.