In Paris, British Prime Minister David Cameron said he will ask for parliamentary approval for the UK to join airstrikes against Islamic State extremists in Syria.
Raids across Brussels capped a tense day with hundreds of troops patrolling and authorities hunting for one or more suspected extremists, including Salah Abdeslam, a fugitive since being named a suspect in the November 13 Paris attacks.
The Belgian government chose to keep the capital on the highest state of alert into the start of the workweek after what it described as a "serious and imminent" threat, preventing a return to normal in the city that is also home to the European Union's main institutions.
Belgian Interior Minister Jan Jambon told the RTL network that Abdeslam "must have a lot of support on our territory. That's why all these searches being conducted at the moment are important."
Also Read
Several of the Paris attackers had lived in Brussels, including Abdelhamid Abaaoud, the plot's orchestrator who was killed Wednesday in a standoff with French police.
Police issued a new appeal to identify the third attacker who was killed in the assault at the national stadium. They posted a photo of the man on Twitter, asking the public for information that would help identify him.
France has intensified its aerial bombing in Syria and Le Drian said the aircraft carrier Charles de Gaulle, which has been sent to the Mediterranean to help combat IS militants in Syria, will be "operational" from Monday and "ready to act."