The Belgian government has allowed the nation to become a breeding ground for ISIS.
The raids came ahead of the arrival of U.S. Secretary of State John Kerry on Friday.
A more integrated Belgium, and Europe, is cited as key to stopping future extremist attacks.
Belgian authorities are facing embarrassment after Turkey said on Wednesday that last year Ankara expelled back to Europe Brahim El Bakraoui.
Pope Francis says arms manufacturers deserve blame for Brussels attacks.
Paris attacks suspect Salah Abdeslam made unassuming Forest his refuge until firefight.
The militant group also uses comments by Donald Trump as part of its propaganda.
"We want to protect Polish citizens from that," a government spokesman said.
Alexey Pushkov said Europe has hushed up links to opposition militants.
The lone surviving attacker from the Paris attacks has also changed his mind about fighting extradition.
A mother of twins, a law student and a government worker were all killed in the bomb blasts.
Our unity in Europe makes us safer, not weaker, says Paddy Ashdown.
With at least 31 dead, Belgians seem resigned to the reality of terror in Europe.
Molenbeek was the location of Salah Abdeslam's arrest, and Schaerbeek was home to the Brussels airport attackers.
Dozens of people died in twin bombings in Brussels on Tuesday.
The top lawmaker on the intelligence committee in the House said the explosion was close to U.S. airline counters.
EU states should "be ashamed" of themselves if they do not cooperate.