Police set up a barricade during an operation in the center of Brussels on Sunday, Nov. 22, 2015 (Photo: AP)
Brussels began a third consecutive day in lockdown under a maximum terror alert Monday after Belgian police staged a series of raids but failed to find key Paris attacks suspect Salah Abdeslam.
In an unprecedented security operation for the European capital, schools, universities and the metro were shut in the face of what Prime Minister Charles Michel called a "serious and imminent" threat of attacks similar to those that killed 130 people in France.
In Paris, Britain's Prime Minister David Cameron accompanied French President Francois Hollande in a visit to the Bataclan concert hall, where 90 people died in by far the bloodiest of the string of attacks claimed by the Islamic State group.
Cameron said on his Twitter account he stood "shoulder to shoulder" with Hollande at the venue, where a British man was among the dead on November 13.
Belgian police on Sunday carried out 19 raids in Brussels and three in the industrial town of Charleroi, detaining 16 people, prosecutors said.
The driver of a car was injured after police fired two shots when the vehicle drove at officers.
"Salah Abdeslam was not caught during the raids," federal prosecutor spokesman Eric Van Der Sypt told reporters just after midnight, meaning Europe's most wanted man remains at large.
Abdeslam's elder brother Brahim blew himself up outside a Paris bar in the November 13 attacks and the 26-year-old is suspected of playing a key role in the massacre.
Armed officers and troops patrolled the near-deserted streets of the tense Belgian capital all weekend after the government raised the terror alert to the highest level of four in the city.
Early Monday morning, traffic was relatively light in the centre of the city and many people opted to cycle to work although most buses were running.
The Brussels-based European Union and NATO both said they would bolster security and urged non-essential staff to work from home on Monday.
Michel said the Brussels metro system would remain shut and schools and universities would be closed over concerns that jihadists were plotting a repeat of the Paris gun and suicide bombing attacks on November 13.
"What we fear are similar attacks, with several individuals in several places," Michel told reporters.
"The threat is considered serious and imminent," he said, adding that the rest of the country, including Brussels airport, would remain on security alert level three, meaning an attack is considered possible and the threat credible.
Officials will review the situation again later Monday.
Interior Minister Jan Jambon earlier said the authorities were looking for "several suspects" and not just for Abdeslam, who is thought to have slipped past French security forces after the Paris attacks.
"The operation is not finished. We will continue until we clean up this mess," Jambon told Belgian radio Monday.
French police meanwhile released a photo of the third of three men who blew themselves up outside France's national stadium during the rampage.
The man in the picture passed through Greece with one of the other suicide bombers, carrying a Syrian passport in the name of Mohammad al-Mahmod, a source close to the investigation said.
Hollande embarked on a diplomatic offensive in a bid to forge a broad anti-IS coalition.
After talks with Cameron, the French leader was due to meet US President Barack Obama on Tuesday and then Germany's Angela Merkel and Russia's Vladimir Putin on the subsequent two days.
The UN Security Council on Friday authorised "all necessary measures" to fight jihadist violence after a wave of deadly attacks, including the downing of a Russian aircraft in Egypt with the loss of 224 lives and the storming of a luxury hotel in Mali that left 19 dead.
Meanwhile, Eagles of Death Metal, the Californian band that was playing at the Bataclan, spoke for the first time since the attacks, with singer Jesse Hughes saying that many fans died trying to protect their friends.
"So many people put themselves in front of people," he said in an excerpt of an interview with Vice News.