Police in Brussels on Thursday launched a desperate hunt for two men suspected of taking part in the bombings that struck at the very heart of Europe

Police in Brussels on Thursday launched a desperate hunt for two men suspected of taking part in the bombings that struck at the very heart of Europe, and were carried out by Takfiri group, ISIL.

Under-fire Belgian security officials are tracking one man identified at the scene of a suicide attack on the metro, as well as a suspected bomber seen on CCTV footage at Brussels airport.

European security authorities faced mounting pressure after it emerged that two brothers who blew themselves up at the airport and on a metro train were known to police and that one of them had been deported from Turkey as a "foreign terrorist fighter".

Flags in the shell-shocked city of Brussels hung at half-mast as Belgium mourned the 31 people from all over the world killed in Tuesday's attacks, while doctors battled to save scores more injured in the carnage.

The latest bombings, coming four months after ISIL militants killed 130 people in a series of attacks in Paris, have raised fears of further strikes in Europe, which is battling to deal with home-grown extremists.

The continent is already fighting crises on several fronts, from its worst refugee crisis since World War II to the possibility of Britain leaving the bloc, and leaders have vowed to combat terrorism "with all means necessary".

EU justice and interior ministers will convene later Thursday in Brussels for an emergency meeting to work out a plan to address the threat to Europe posed by jihadists and the application of anti-terrorism laws across the bloc.

On Wednesday, prosecutors said brothers Ibrahim and Khalid El Bakraoui had carried out attacks at Zaventem airport and Maalbeek station, while police sources named bomb-maker Najim Laachraoui as a second airport bomber.

Police have launched a massive manhunt for the third airport suspect, seen wearing a hat and white jacket on CCTV footage from Zaventem departure hall, whose explosive-packed luggage failed to go off with the two other suicide bombers.

It has emerged that the three men identified have links to the Paris attacks in November, underscoring the threat European nations face from the Takfiri group.