An image widely published by Belgian media is said to show three men who are believed to have carried out the attack at Zaventem Airport, BBC reports.

BRUSSELS - Belgian police identified two suspected Islamic State suicide bombers captured on security cameras before they struck Brussels Airport on Tuesday in the first of two attacks that also hit the city's metro, public broadcaster RTBF said on Wednesday.

The death toll in the attacks on the Belgian capital, home to the European Union institutions and NATO, rose to at least 31 with more than 200 wounded, Health Minister Maggie De Block said on VRT television.

The Syrian-based Islamist militant group claimed responsibility four days after the arrest in Brussels of a prime suspect in November's Paris attacks. If confirmed, the identifications would link the Brussels blasts directly to the jailed Paris suspect, Salah Abdeslam.

The attacks sent shockwaves across Europe and around the world, with authorities racing to review security at airports and on public transport, and rekindled debate about European security cooperation and police methods.

RTBF, quoting a police source, named the suspected bombers as Khalid and Brahim El Bakraoui, two brothers resident in Brussels and known to the security services for crime.

The newspaper DH said a third suspect seen with them before running away from the airport after the blasts was identified as Najim Laachraoui, 25, a man sought by police and directly linked to Abdeslam.

Khalid had rented under a false name the apartment in the city's Forest borough, where police hunting Abdeslam killed a gunman in a raid last week, RTBF said.

Brussels police searched a house in the north of the city late into the night, turning up another bomb, an Islamic State flag and bomb-making chemicals in an apartment in the borough of Schaerbeek.

Local media said authorities had followed a tip from a taxi driver who may have driven the bombers to the airport.

Investigators said they were focusing on a man in a hat who was caught on CCTV pushing a laden baggage trolley at the airport with two others they believed were the bombers. An unused explosive device was later found at the airport and the man, believed to be Laachraoui, was seen running away from the terminal after the explosions.

Belgium is observing three days of national mourning. A minute's silence for the victims will be held at midday.