Foreign Minister Julie Bishop issued a swift condemnation of the attacks and said her department was "urgently seeking" to find out if any Australians were affected. Emergency rescue workers stretcher a person at the site of an explosion at a metro station in Brussels. Credit:AP The fact that authorities were still failing to contain the wave of violent extremism even after the November Paris attacks and subsequent massive manhunt that netted the final Paris plotter, Salah Abdeslam, just five days ago suggested the problem was beyond the security agencies of Belgium and its neighbours, experts said. Edwin Bakker, director of the Centre for Terrorism and Counter Terrorism at Leiden University in The Hague, said with the highest number per capita of extremists travelling to and from Syria, Belgium seemed to have lost control of the problem. "Apparently the intelligence position is not good enough to find these people or even to find the most wanted terrorist in Europe," he said of Abdeslam, the Belgian-born French suspect who was arrested on Friday after a four-month manhunt.

"It took them several months and this guy was not hiding on his own. That makes it a bit embarrassing for the intelligence community in Belgium. People walk away from Brussels airport after the blasts. Credit:Geert Vanden Wijngaert "The events of today increase both worries about the intelligence position of Belgian authorities as well as how many supporters there are. "They're not that amateuristic either. These support groups are a big worry and in some countries they run in the hundreds if not the thousands and that's too many for the authorities to monitor." People comfort one another outside Brussels airport. Credit:AP

More concerning still, it was not just Belgian authorities but French agencies who were involved in hunting Abdeslam and trying to break up the extensive networks of which he was part. "You hope the Muslim communities will be their eyes and ears but apparently that didn't happen so there are a lot of worries," Professor Bakker said. Belgian Interior Minister Jan Jambon admitted after the Paris attacks that "we don't have a grip on the situation in Molenbeek". The district was home to the now-banned group Sharia4Belgium, seen as an incubator for Brussels' radical scene, and has been the source of several plots in addition to Paris. Professor Bakker meanwhile said that Belgian authorities had been slow to respond to the rising extremism problem. They had "neglected their intelligence capacity for a long time" and suffered political divisions across the French-Flemish political blocs, which hampered communication and a sense of common purpose, he said.

Both Professor Bakker and Monash University terrorism expert Greg Barton said there was a strong chance that the Brussels attacks were carried out by extremists who were on the run after the Abdeslam arrest and decided they might as well launch the assault before they were caught. Professor Barton said it was "almost certain" the attack was linked to associates of Abdeslam's, perhaps those who'd fled before police launched the raid that captured the Paris attacker in the notorious Molenbeek district of Brussels. "Given they haven't arrested other people, it seems very likely those people decided they would attack before they were arrested, thinking it was better to attack and achieve something." He said a 55-page report released last week on the Paris attacks showed French authorities had been "surprised at how extensive this network was, and that it was more professional than they expected". Tuesday's attack "suggests there is still a fair part of this network in Brussels", he said.

"This is a scale of threat that has gone beyond both Belgian and French authorities," he said. He said it was "wrong to paint the Belgian authorities as completely hopeless". "All of us have been caught by how quickly this has grown and how big it has become with the Islamic State." The "technocratic" nature of the organisation causing ructions in Syria and Iraq appeared to extend even to these remote attacks on the West, he said. Raffaello Pantucci, director of international security studies at the Royal United Services Institute, said Abdeslam's arrest may have accelerated existing plans for the attacks, with the plotters fearing that Abdeslam would reveal their plans in interrogation by security services.

Loading "When Abdeslam gets arrested, you will have the network around him all starting to panic," he told British newspaper the Daily Express. "If you have problems building up, or people thinking about doing stuff, they might accelerate any planned attacks."