BRUSSELS - Police issued a wanted notice for a man suspected of involvement in Tuesday's bomb attacks at Brussels airport that left at least 10 people dead.
Calling for information, they issued a photograph of a man, dressed in a white shirt and jacket and wearing a dark hat, as he pushed a luggage trolley through the airport.
In joint attacks on Tuesday, a second blast on a rush-hour train also killed a further 20 people.
Broadcasters RTL and RTBF reported anti-terrorist police were carrying out searches in the Brussels district of Schaerbeek and Jette.
Belgian media earlier carried pictures from airport security cameras showing two people in black and a third person wearing a hat and following just behind.
Islamic State claimed responsibility for the attacks the group said in a statement released on its official Telegram account.
"We promise the crusader alliance against the Islamic State that they will have black days in return for their aggression against the Islamic State," the jihadist group said.
Before the statement was released the AMAQ news agency close to the group reported that, "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," Amaq said.
Immediately following the attacks, ISIS adherents on social media were celebrating.
The blasts at the airport and metro station occurred four days after the arrest in Brussels of a suspected participant in the November ISIS attacks in Paris that killed 130 people. Belgian police had been on alert for any reprisal action.
Shortly after the first explosion in Zaventem airport Islamic State's supporters created the Twitter hashtag, "Brussels is on fire," to express their happiness in light of the attack and deliver threatening messages to "Western Crusaders."
The most common remark under the hashtag was "You declared war against us and bombed us, and we attack you inside your homeland." After each additional attack, ISIS supporters celebrated writing "Allahu Akbar."
The popular hashtag is apparently inspired by a similar hashtag created by ISIS supporters after the November 13 Paris terror attacks, "Paris is on fire."
US AIRPORTS ON EDGE AFTER ATTACKS
Airports in major US cities were on high alert on Tuesday, with police out in force after the bombings, though officials said there was no specific threat to the United States.
The Obama administration was expected to tighten security at US airports following the Brussels airport attack, which occurred in a public hall outside of the security check area.
US Representative Adam Schiff of California, the ranking Democrat on the House intelligence committee, said he was concerned that there was a risk of copy cat attacks and that airport security was still a concern despite changes in recent years.
"Overall though there's a lot more work we still need to do at our airports," Schiff told MSNBC.
Delta Air Lines Inc, United Continental Holdings Inc and American Airlines Group Inc reported that they had canceled or rerouted flights as a result of the attack.
Large numbers of uniformed police officers, some in tactical gear as well as National Guard members in fatigues and carrying long weapons, were on patrol at New York's John F. Kennedy International Airport.
One guard member was overheard telling a colleague "we have to keep an eye out for bags" after reports that many of the wounded at the Brussels airport had severe leg injuries, according to officials, a pattern that suggests an explosion at ground-level, possibly from a bag.
Some travelers in the United States said they hoped airports would further tighten security following the Brussels attack.
"Perhaps it should take place sooner, before you get through security. I find it reassuring," said Mary Ray, 71, a retired government trainer flying home to Manchester, England, from New York after a Caribbean cruise with her husband, Malcolm.
Ray said she is happy to remove her shoes or have her hands swabbed as she passes through airport security: "I think it's a deterrent."