ISIS supporters have been celebrating the Brussels attacks online as speculation mounts that the group is behind a wave of deadly attacks in the Belgian capital.

There was no immediate claim of responsibility in the wake of three bombings at the city’s airport and a Metro station on Tuesday morning but the timing, coming days after the arrest of Paris attacks suspect Salah Abdeslam was considered significant.

As the death toll rose amid continuing rescue operations, supporters of the so-called Islamic State were championing the attacks on Twitter.

 “What a beautiful day today,” one man wrote, calling the victims “Belgium supporters” who did not count as civilians.

“F*** Belgium. Belgium wanted to bomb the Islamic state Now enjoy what your hands have sown.

“A lot of duas [prayers] were answered today.”

The supporter claimed to have received a message from an Isis militant to the group’s supporters in Belgium reading: “We have come to you with slaughter.”

The claims could not be confirmed and Isis supporters are known for claiming responsibility for terror attacks around the world without offering proof.

Charlie Winter, a terrorism analyst and senior research associate at Georgia State University, said there was no official claim from Isis in the hours after the explosions.

“Lots of fanboy noise, but no statement,” he added on Twitter.

Official claims usually come from the Amaq Agency and Isis’ other propaganda outlets, which were silent on Brussels on Tuesday morning even while publishing details of other alleged operations in Iraq and Syria.

Alongside al-Qaeda, Isis is considered one of the few international terrorist organisations with the means and manpower to target a European city on this scale.

Investigations into the massacres that killed 130 people in Paris in November uncovered a wide network of hideouts and safe houses across France and Belgium, including a bomb-making factory concealed inside a flat.

Isis released its official claim of responsibility for those attacks the following morning, spreading audio and written statements in Arabic, French and English claiming the “blessed battle” was an act of revenge for France’s involvement in the US-led coalition bombing its militants in Iraq and Syria.

But its statement exaggerated the death toll of the massacres and listed shootings in the 18th arrondissement, where there was no attack.

If the group is responsible for Tuesday’s bombings, it may be delaying any announcement until its planned attacks are over and militants are all killed or have escaped.

The Belgian foreign minister, Didier Reynders, said authorities feared an unknown number of attackers or accomplices were still at large several hours after the explosions.

Dr Natasha Underhill, an expert on terrorism in the Middle East at Nottingham Trent University, said there was “little doubt” that the latest atrocity in Europe was linked to Isis or its affiliates.

“It should, in some ways, have come as no surprise that there would have been some reaction from the group in response to the capture of Salah Abdeslam,” she added.

“This was no doubt a warning strike to European leaders and there may be more to come. The group has time and time again issued statements that it will have no mercy in targeting those who are supporting the US and who are fighting against the group. 

“The likelihood of further attacks in Europe is now in very little doubt. 

“The promotion of fear is one of the strongest assets that Islamic State possesses and it is sadly doing an excellent job in spreading this message across Europe.”

Michael Horowitz, a security analyst with the Levantine Group, cautioned against blaming the attack on Abdeslam’s arrest in Molenbeek on Friday.“Very unlikely that such a large scale attack was a ‘retaliation’ to Salah Abdeslam's arrest as some are claiming,” he wrote on Twitter.

“Attack was likely planned months ago, possibility that Abdeslam was going to talk and give intel about the cell likely triggered the attack.”

The 26-year-old militant had reportedly told investigators he was part of a cell planning further atrocities in Brussels after a large cache of weapons was found.

The terror alert has been increased to its highest level in Belgium as police operations continue, with Brussels airport, public transport systems, federal buildings closed.

Security has been increased at airports and transport hubs across Europe as investigations continue.

Courtesy The Independent