Six people were arrested in a series of police raids in Brussels, federal prosecutors said, two days after jihadist attacks in the Belgian capital left 31 dead.
The arrests come as Belgian ministers under fire for intelligence failings over Tuesday's Islamic State-claimed suicide blasts admitted "errors" and offered to quit.
Prime Minister Charles Michel refused to accept the resignations of the interior and justice ministers, who have been severely criticised for allowing the attackers -- at least three of whom were known to authorities -- to slip through the net.
Hundreds of people gathered late into the night at the Place de la Bourse in Brussels to mourn the victims of the suicide attacks on the city's airport and metro on Tuesday.
"Our love for Brussels is stronger than terror," read a banner held by a young couple.
Led by King Philippe, Belgians also observed a minute of silence on the third and final day of mourning for the 31 people killed and 300 injured in attacks.
Harrowing new footage of the moments after the Zaventem airport attack meanwhile emerged on Belgian television, showing a lone baby left crying in the wreckage next to the lifeless body of a woman.
With criticism growing that international authorities failed to follow links between Tuesday's bombings and the attacks on France in November, key Paris suspect Salah Abdeslam insisted he was unaware of plans to strike the Belgian capital.
Police arrested Abdeslam in Brussels on Friday, after he spent four months on the run as the last surviving member of the group that killed 130 people in Paris.
Abdeslam's lawyer Sven Mary said Thursday his client now did not want to fight extradition to Paris and insisted he "didn't know" in advance about the Brussels attacks.
But Belgium is reeling from revelations that three of the Brussels attackers -- including Ibrahim El Bakraoui and his brother Khalid, who bombed Maalbeek metro station -- were known to police and had strong links to Abdeslam.
Interior minister Jan Jambon and Justice Minister Koen Geens both tendered their resignations over the claims that Ibrahim El Bakraoui had slipped through the net despite being arrested by Turkey near the Syrian border and deported to the Netherlands.
"There were errors at Justice and with the (Belgian) liaison officer in Turkey," Jambon was quoted as telling the Le Soir daily.
Prosecutors meanwhile confirmed that Khalid El Bakraoui was the subject of an international warrant for terrorism in relation to the Paris attacks and had rented out a flat used by the Paris cell in the Belgian city of Charleroi.
