Revealed: Terror attack was ‘revenge’ for arrest of Europe’s most wanted man... but was Belgian bloodbath triggered EARLY because fanatics feared Paris jihadi Abdeslam would betray them?

Europe’s security services had feared a bloody terrorist outrage in Brussels since the high-profile arrest of Paris failed suicide bomber Salah Abdeslam in the city four days ago. 

Intelligence officers today described the attacks in the Belgian capital as ‘sadly expected’ both as a ‘revenge’ for the arrest of Europe’s most wanted man but also ironically because the jihadists knew that HE could betray them. 

For while the Brussels-born Islamist had become a symbol of defiance for the jihadist movement and Islamic State during his extraordinary four months on the run under the noses of Belgium’s biggest manhunt, his dramatic arrest on a street in the Molenbeek district of the city also signalled the net could be closing on those he had plotted with. 

Arrested: Failed Paris suicide bomber Salah Abdeslam was arrested in Brussels four days ago 

Manhunt: He had eluded security forces for four months while he hid among friends in the Belgian city

Betrayal: But now intelligence officers say today's attacks may have been fast tracked as his arrest meant authorities would be closer to closing in on other Brussels IS sleeper cells he is associated with 

Crucially, Belgian investigators had already suggested that Abdeslam was co-operating with them and his fellow jihadists would have known that he could betray them – and their plans. 

Intelligence officers told MailOnline the concerns of his fellow terrorists would have been fuelled by the fact that twice Abdeslam had ‘pulled back’ from killing himself by triggering a suicide vest – once in Paris and again on the day of his arrest. 

‘This showed a weakness, a desire to live which would have been played on during questioning,’ an anti-terror specialist said today. 

‘He was not a man showing inner strength and the capacity to withstand interrogation, this meant that if those involved in today’s attacks were known to him they believed they had to activate their plans before they too were arrested and their weapons seized.’ 

Terror: This morning's attacks at Zaventem Airport (pictured) and Maelbeek are believed have been carried out by Islamist extremists, although no group has yet claimed responsibility for the suicide attacks

Murder: The attacks have killed at least 34 people across the city and seriously wounded dozens more 

Mobile telephones, laptops and CCTV footage recovered from the basement apartment Abdeslam was hiding in are also likely to have provided clues as to the identities and locations of fellow terror suspects, many of them living in Molenbeek which is seen by many investigators as being the ‘heart’ of IS operations in Europe . 

Detained: Anti-terror specialists say Salah Abdesalam was not willing to blow himself up during the Paris attacks

‘At this stage we can’t be sure those behind today’s attacks are directly associated with Abdeslam but it is certainly fair to say the suicide attacks will be linked to his detention,’ the anti-terror specialist added. 

‘They send a clear message to the authorities that they have arrested a well-known suspect but there are many more out there prepared to do what Abdeslam was not willing to do: blow himself up. 

'They will know that this is the hardest thing to stop and there are still a lot of explosive devices out there.’ 

He added: ‘There is the obvious fear that this is only the beginning of attacks against soft targets both in Belgium and elsewhere in Europe. A departure lounge, like a tube station, is an easy target but it also has the ‘advantage’ from the terrorist perspective of a focused attack – the chances are there would be Americans – the priority for IS - waiting to check-in at an American Airlines desk.’ 

Abdeslam is believed to be the sole survivor of the 10 men who were directly involved in the attacks that killed 130 people in and around Paris on November 13. 

A suicide vest was said to have been found in the Molenbeek flat where Abdeslam had been sheltered and similar devices have been seized in other raids as well as having been used in the Stade de France bombings last November. 

Traced: Authorities are likely to focus attention on the Molenbeek district of Brussels, where most Belgian's who travel to Syria and Iraq to join ISIS originate - including Salah Abdesalam 

That flat was rented by Islamist Najim Laachraoui, who used the alias Soufiane Kayal, who was with Abdeslam in Hungary weeks earlier and whose whereabouts are unknown.

Investigators will want to know if he was linked to today’s attacks. 

It is in this district that much of the investigation into the Brussels attacks will initially focus with Belgian officers – severely criticised for their embarrassing failure to arrest one of the world’s most wanted men when he was living just a few streets from his old home – seeking to identify the suicide bombers. 

They will be aided by the fact that both Zaventem airport and the underground are extensively covered by security cameras which are believed to have captured at least one of the bombers shortly before the suicide belt was triggered. 

Officers will work on tracing back the movements of the bombers from their targets to the minutes before, identifying how they travelled - were they dropped off and if so, by who ? Did they use public transport or a private car as in the Paris atrocities? 

They will seek to answer when the bombers travelled, how they concealed their devices and whether they were linked to so-called ‘chatter’ monitored by security officials pointing towards an attack in some form. 

Fear: Experts say this could be the beginning of attacks against 'soft' targets in Belgium and Europe

Abdesalam was found in a flat rented by accomplice Najim Laachraoui, 24, also known as Soufiane Kayal

Linked: Investigators will still hunt Najim Laachraoui, and Mohamad Abrini - accomplices in the Paris attack

Investigators will also establish whether they make the ‘mistake’ of carrying mobile telephones – it was through one discarded phone thrown in a bin by a bomber minutes before he blew himself up that some of the key figures in the Paris attacks were hunted down. 

Police will seek to discover where they began their journey – and if they were on the radar of Belgian and French investigators or if they were so-called ‘clean skins’ not previously known to police. 

A number of ‘sleeper cells’ are suspected to be hiding in Belgium. At least two suspected terror cells are said to have been under surveillance by the Belgian authorities while French police are said to be monitoring dozens of men and women ‘of interest’ in and around Paris. 

The UK’s communication headquarters in Cheltenham is said to have been helping with the monitoring of messages sent from Syria and Iraq to Europe. 

Intelligence is said to have been ‘shared’ with Belgium, France, Germany and Holland as well as the United States in recent days. Britain has a huge on-going surveillance operation focused on jihadi suspects and their supporters, some of who have links to Belgium and France. 

Mohamed Abrini, 31, (pictured right) was filmed with Abdeslam at a petrol station on a highway to Paris two days before the Paris attacks. Left, Najim Laachraoui

This includes military specialists in surveillance and ‘deep cover’ seconded to the police and MI5. The SAS and SBS are both on standby in case of attack or their expertise is needed alongside the police firearms teams. 

On Monday, the Belgian authorities asked for the public’s help in finding Najim Laachraoui, 24, who they identified as an accomplice of Abdeslam. 

The authorities are also searching for Mohamed Abrini, 31, who was filmed with Abdeslam at a petrol station on a highway to Paris two days before the Paris attacks. 

There is said to have been concern too in recent days of jihadist sympathisers travelling from both Germany and Serbia into Belgium across its porous borders.

These include routes used by migrants and there will be concern that IS ‘plants’ may have been among the bombers. Witnesses have claimed that one of the suicide bombers was speaking Arabic shortly before the blast. 

With hundreds of Belgians – many of North African origin – travelling to Syria in order to fight for IS and other jihadi groups, there has been an extensive operation to identify those returning. 

Aided by intelligence supplied by countries, including Britain, dozens are said to have been identified as returning but, alarmingly, their locations in several cases are unknown. 

This is also the case in other European countries where suspects are said to be ‘missing’ and frantic attempts are underway to trace them, including the use of voice recognition on telephones. Several are suspected of links to Molenbeek where investigators say a number of ‘sleeper cells’ are thought to be awaiting orders.  

Return: According to intelligence dozens of jihadis are said to be returning to their home countries 

Abdeslam, officers said yesterday, with his own close links to Syria, may have been among those helping to co-ordinate them or because of his trusted position, choosing targets. 

The district with thousands of immigrants - approximately half are of Muslim descent and in some parts 70-80 per cent - has a history of links with extremism.

It was searched as part of anti-terror operations that were carried out in Belgium in the wake of the Charlie Hebdo attacks.

A suspect in a foiled attack on a high-speed train from Belgium to France was reported to have stayed at his sister's house in Molenbeek, while a Frenchman accused of shooting dead four people last year at the Jewish Museum in Brussels also spent time in the area.

Belgium's Interior Minister Jan Jambon admitted a high proportion of those who have left Belgium to join Islamist groups came from the area, and recently vowed to ‘clean it up.’ 

‘The number of people going to Syria has gone down,’ he said. ‘But those who go, still come from Molenbeek and Brussels.’ 

Significantly, Brussels and Molenbeek are also seen as a target for weapons smugglers – the guns linked mainly not to terrorism but to serious crime. Weapons from there have been implicated in crimes in the UK, investigators say. 

While most of the weapons are handguns, Belgian police have noticed an increase in the possession and use of military-style weapons such as Kalashnikovs. 

Depending on the type and condition of the weapon, prices on the Belgian black market are generally between 1,000 and 2,000 euro (£700-£1,400). 

Many of the weapons have been smuggled from the Balkans where huge numbers of guns, together with ammunition and explosives have been left over after the wars there.