Belgian police searching for Najim Laachraoui, third suspect connected to Brussels attack

European authorities believe two brothers with ties to the Islamic State and the plotters of the November Paris attacks were among the suicide bombers who blew themselves up in Brussels on Tuesday and that the third suspect who helped them is now on the run in the Belgian capital.

With an intense manhunt underway Wednesday, officials said brothers Brahim and Khalid El Bakraoui were responsible for one of the two blasts that killed 14 people at Brussels’ international airport, as well as the explosion that ripped through a metro train killing another 17 people.

The Belgian news outlet RTBF reported that Brahim El Bakraoui was one of three men seen on closed-circuit television at the airport pushing a baggage trolley moments before the explosions hit. The Islamic State, also known as ISIS and ISIL, has claimed responsibility for the attacks.

The death toll in the strikes on the Belgian capital, home to the European Union and NATO, rose to at least 31 with some 260 wounded on Wednesday — a toll that’s expected to rise further because some victims were blown to pieces making it difficult to confirm identities.

With that as a backdrop, investigators were scrambling to identify the second airport bomber on Wednesday. Authorities in Brussels said that another suspect, 25-year-old Najim Laachraoui, is believed to be on the run and that he too has a connection to the Paris attacks.

Mr. Laachraoui has been on the radar of investigators for months, since his DNA was found on at least two explosives belts that were used in the wave of bombings that hit Paris in November.

But Belgian officials ratcheted up their search for him last week, after his DNA was also found at a Brussels hideout known to have been used by the high-profile Paris attack suspect that authorities arrested last week.

Salah Abdeslam, who is believed to be the lone surviving member of the team of terrorists that hit Paris in November, was taken into custody in Brussels on Friday after a shoot-out with police.

He has reportedly been co-operating with investigators since, and his statements in custody are believed to be what led top Belgian officials to warn ahead of Tuesday’s strikes that ISIS could attack in retaliation for his arrest.

In addition to the Laachraoui-Abdeslam connection, meanwhile, reports also point to ties between the Paris attacks and the El Bakraoui brothers.

RTBF’s report said Khalid El Bakraoui had rented under a false name the apartment where police killed a gunman while hunting for Mr. Abdeslam last week. The report said El Bakraoui is also believed to have rented a safe house in the southern Belgian city of Charleroi, used to mount the Paris attacks.

• This article is based in part on wire service reports.