Belgian authorities published surveillance camera images of three suspects in the attack on Brussels airport on Tuesday, Belga news agency reported.
The Islamic State claimed responsibility for attacks on the airport and a rush-hour metro train in the Belgian capital which killed more than 30 people, a news agency affiliated to the group said.
The grainy picture, which Belga said was released by Belgian police at the request of the federal prosecutor, shows three men pushing trollies with suitcases past the check-in area. Two have dark hair and one is wearing a hat.
More than 200 people were wounded in the bloodshed, which came just four days after the dramatic arrest in Brussels of Salah Abdeslam, the prime suspect in the Paris attacks last November.
The fact that extremists were able to hit high-profile targets in Brussels, Europe’s symbolic capital, just months after IS militants killed 130 people in Paris, will raise fresh questions about the continent’s ability to cope with the terror threat.
There are fears more suspects could still be at large in Brussels, home to the headquarters of both NATO and the European Union, Belgian foreign minister Didier Reynders warned.
The Amaq agency said suicide bombers from IS, strapped into explosive belts, staged Tuesday’s attacks. Belgian media said police were hunting one attacker who had survived.
Amaq carried the claim of responsibility and said: “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.”
Public broadcaster VRT said police had found a Kalashnikov assault rifle next to the body of an attacker at the airport.
Such weapons have become a trademark of IS-inspired attacks in Europe, notably in Belgium and France, including on November 13 in Paris.
An unused explosive belt was also found in the area, the public broadcaster said. Police were continuing to scour the airport for any further bombs or attackers.
‘We are at war’
The coordinated assault triggered security alerts across Europe and drew global expressions of support.
Authorities appealed to citizens not to use overloaded telephone networks, extra troops were sent into the city and the Belgian Crisis Centre, clearly wary of a further incident, appealed to the population: “Stay where you are”.
“We are at war and we have been subjected to acts of war in Europe for the last few months,” French Prime Minister Manuel Valls said.
Brussels airport will remain closed on Wednesday, its chief executive Arnaud Feist told reporters.
The complex was evacuated and trains to the airport stopped. Passengers were taken to coaches from the terminal that would remove them to a secure area.
All three main long-distance rail stations in Brussels were closed and train services on the cross-channel tunnel from London to Brussels were suspended.
Security services have been on a high state of alert across western Europe for fear of militant attacks backed by IS.
While most European airports are known for stringent screening procedures of passengers and their baggage, that typically takes place only once passengers have checked in and are heading to the departure gates.
Although there may be discreet surveillance, there is nothing to prevent members of the public walking in to the departure hall at Zaventem airport with heavy baggage.
Following an attempted ramraid attack at Glasgow Airport in 2007, several airports stepped up security at entrances by altering the pick-up and drop-off zones to prevent private cars getting too close to terminal buildings.
European stocks fell after the Brussels explosions, particularly travel sector stocks including airlines and hotels, pulling the broader indices down from multi-week highs. Safe-haven assets, gold and government bonds rose in price.
Belgium’s interior minister, Jan Jambon, said on Monday the country was on high alert for a revenge attack in the wake of Abdeslam arrest.
It was not clear what failings if any allowed the plan for Tuesday’s operation to go ahead and whether the double attack was planned in advance or put together at short notice.
“We know that stopping one cell can ... push others into action. We are aware of it in this case,” Jambon said.
‘Whole of Europe hit’
Leaders across Europe reacted with outrage to the attack, urging closer counter-terror cooperation on a continent that has been on high alert for months.
“The whole of Europe has been hit,” said French President Francois Hollande, whose country is still reeling from November’s attacks.
British Prime Minister David Cameron warned of the “very real” terrorist threat faced by countries across Europe, declaring: “We will never left these terrorists win.”
US President Barack Obama said Washington stood with Belgium in the face of the “outrageous” attacks.
“We will do whatever is necessary to support our friend and ally Belgium in bringing to justice those who are responsible, and this is yet another reminder that the world must unite,” Obama said.
Security was also beefed up at Belgium’s nuclear plants and at EU buildings in the French city of Strasbourg, home to the European Parliament.
Messages of solidarity poured out on social media, with thousands of people sharing images of beloved Belgian cartoon character Tintin in tears.
I still loved London after 7/7. I loved it more. I'll continue to live in Brussels as I love Belgium. Safe & sad. pic.twitter.com/66PWttTC2C— Union Bruxelles Man (@UnionBerlinMan) March 22, 2016
It has been a week of drama and bloodshed in Brussels. Last Tuesday saw a shootout in the city’s south that saw a Kalashnikov-wielding man killed and four police officers wounded.
Investigators believe key Paris suspect Abdeslam slipped out of the apartment as the gun battle broke out. He was arrested three days later in Brussels’ gritty Molenbeek district -- just around the corner from his family home.
Shiraz Maher, a radicalisation expert at Kings College London, said it was “very likely that this attack will have been planned and prepared well in advance of last week’s arrest of Salah Abdeslam”.
The bombings came at a time when the brutal jihadist group is under pressure and losing territory in its strongholds in Iraq and Syria.
Read: Who is Salah Abdeslam?