BRUSSELS (Reuters) – Islamic State claimed responsibility for suicide bomb attacks on Brussels airport and a rush-hour metro train in the Belgian capital on Tuesday which killed at least 30 people, with police hunting a suspect who fled the air terminal.

Police issued a wanted notice for a young man in a hat who was caught on CCTV pushing a laden luggage trolley at Zaventem airport alongside two others who, investigators said, had later blown themselves up in the terminal, killing at least 10 people.

Officials said 20 died on the metro train close to European Union institutions, and Islamic State said that too was a suicide attack.

The coordinated assault triggered security alerts across Europe and drew global expressions of support, four days after Brussels police had captured the prime surviving suspect in Islamic State’s attacks on Paris last November.

Belgian authorities were still checking whether the attacks were linked to the arrest of Salah Abdeslam, according to Federal Prosecutor Frederic Van Leeuw, although U.S. officials said the level of organization involved suggested they had previously been in preparation.

Last week, explosives and an Islamic flag were found during a raid on a Brussels flat. Police also found a fresh fingerprint of Abdeslam’s there, putting them on to his trail. It was not clear if Abdeslam had been involved at that stage in planning the airport attack.

In a statement, Islamic State said “caliphate soldiers, strapped with suicide vests and carrying explosive devices and machineguns” had targeted the airport and metro station, adding that they had set off their vests amidst the crowds.

A bomb and an Islamic State flag were also found on Tuesday in a flat in Brussels, and Van Leeuw confirmed a manhunt was under way. “A photograph of three male suspects was taken at Zaventem. Two of them seem to have committed suicide attacks. The third, wearing a light-colored jacket and a hat, is actively being sought,” he told a news conference.

A government official said the third suspect had been seen running away from the airport building. Local media reported police had found an undetonated suicide vest in the area.

Belgian police appealed to travelers who had been at the airport and metro station to send in any photographs taken before the attacks in their efforts to identify the bombers.

After questioning Abdeslam, police issued a wanted notice on Monday, identifying 25-year-old Najim Laachraoui as linked to the Paris attacks. The poor quality of Tuesday’s CCTV images and of the Laachraoui wanted poster left open whether he might be the person caught on the airport cameras.

Citizens of the United States, Spain and Sweden were among the injured, their governments reported.

SHOUTS IN ARABIC

A witness said he heard shouts in Arabic and shots shortly before two blasts struck in a packed airport departure lounge at the airport.

Belgian media published the security camera picture of three young men pushing laden luggage trolleys. Police later issued a cropped version of the same photograph, showing only one of the three.

“If you recognize this individual or if you have information on this attack, please contact the investigators,” the notice read. “Discretion assured.”

Police operations were under way at several points in the city but a lockdown imposed immediately after the attacks was eased and commuters and students headed home as public transport partially reopened.

In its statement, Islamic State said: “We promise the crusader alliance against the Islamic State that they will have black days in return for their aggression against the Islamic State.”

Belgium, home to the EU and the headquarters of the NATO military alliance, has sent warplanes to take part in operations against Islamic State in the Middle East.

Austrian Horst Pilger, who was awaiting a flight with his family when the attackers struck, said his children had thought fireworks were going off, but he instantly knew an assault was underway.

“My wife and I both thought ‘bomb’. We looked into each other’s eyes,” he told Reuters. “Five or 10 seconds later there was a major, major, major blast in close vicinity. It was massive.”

Pilger, who works at the European Commission, said the whole ceiling collapsed and smoke flooded the building.

Security services found and destroyed a third bomb at the airport.

“BLACK MOMENT”

U.S. President Barack Obama led calls of support to Belgian Prime Minister Charles Michel after Brussels had gone into a state of virtual lock-down.

“We must be together regardless of nationality or race or faith in fighting against the scourge of terrorism,” Obama told a news conference in Cuba. “We can and we will defeat those who threaten the safety and security of people all around the world.”

Michel spoke at a Brussels news conference of a “black moment” for his country. “What we had feared has come to pass.”

In Paris, where Islamic State killed 130 people in November, the Eiffel Tower was lit up with the colors of the Belgian flag on Tuesday evening in a show of solidarity with Brussels.

Brussels airport will remain closed on Wednesday, its chief executive Arnaud Feist told reporters.

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 Islamic State-inspired attacks in Europe, notably in Belgium and France, including on Nov. 13 in Paris.

Alphonse Youla, 40, who works at the airport, told Reuters he heard a man shouting out in Arabic before the first explosion. “Then the glass ceiling of the airport collapsed.”

“I helped carry out five people dead, their legs destroyed,” he said, his hands covered in blood.

Others said they also heard shooting before the blasts.

A witness said the blasts occurred at a check-in desk.

Video showed devastation in the hall with ceiling tiles and glass scattered across the floor. Bloodied bodies lay around.

Some passengers emerged from the terminal with blood spattered over their clothes. Smoke rose from the building through shattered windows and passengers fled down a slipway, some still hauling their bags.

Britain, Germany, France and the Netherlands, all wary of spillover from conflict in Syria, were among states announcing extra security measures. Security was tightened at the Dutch border with Belgium.

The blast hit the train as it left Maelbeek station, close to EU institutions, heading to the city center.

VRT carried a photograph of a metro carriage at a platform with doors and windows completely blown out, its structure deformed and interior mangled and charred.

A local journalist tweeted a photograph of a person lying covered in blood among smoke outside the station. Ambulances were ferrying the wounded away and sirens rang out across the area.

“WE ARE AT WAR”

“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.

Train services on the cross-channel tunnel from London to Brussels were suspended. Britain advised its citizens to avoid all but essential travel to Brussels.

Security services have been on a high state of alert across western Europe for fear of militant attacks backed by Islamic State, which claimed responsibility for the Paris attack.

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.

Abdeslam, the prime surviving suspect for the Paris attacks on a stadium, cafes and a concert hall, was captured by Belgian police after a shootout on Friday. Interior Minister, Jan Jambon, said on Monday the country was on high alert for a revenge attack.

(Additional reporting by Andrew Heavens in London, Ali Abdelaty and Eric Knecht in Cairo, Barbara Lewis, Robert-Jan Bartunek, Clement Rossignol, Julia Fioretti, Meredith McGrath, Foo Yun Chee, Robin Emmott, Jan Strupczewski, Bate Felix and Alastair Macdonald in Brussels and Jochen Elegeert in Amsterdam; Editing by Ralph Boulton and David Stamp)