In a statement released through one of its propaganda outlets, the so-called Islamic State said "explosive belts and devices" were used to massacre passengers checking in at Brussels Airport and on a Metro train.
"Islamic State fighters opened fire inside Zaventem Airport, before several of them detonated their explosive belts, as a martyrdom bomber detonated his explosive belt in the Maalbeek Metro station," a spokesperson said.
The group claimed that the attacks left more than 230 dead and wounded, although Belgian authorities put the figure slightly lower at at least 31 killed and under 200 injured.
It said Belgium was targeted as "a country participating in the international coalition against the Islamic State", although the country only carried out a limited bombing campaign confined to Iraq before stopping its air strikes in June 2015.
More than 100 supporting troops and military advisers are believed to remain in the country.
The timing of the attacks, coming days after the arrest of Paris attacks suspect Salah Abdeslam was considered significant but no mention of the captured militant was made.
As the death toll rose amid continuing rescue operations, Isis supporters 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.”
In Arabic, the hashtag #Brusselsonfire was being used by those praising the slaughter in a similar wording to the #Parisonfire trend seen when the French capital was hit.
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.
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 would not be the last.
“The likelihood of further attacks in Europe is now in very little doubt,” she added.
“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.”
Abdeslam, the only surviving attacker from Isis’ massacres in Paris in November, had reportedly told investigators he was part of a cell planning further atrocities in Brussels after a large cache of weapons was found.
Security has been increased at airports and transport hubs across Europe as investigations continue.
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