Brussels airport officials say flights won't resume before Tuesday as they assess the damage caused by twin explosions in the terminal earlier this week.
Police raided Brussels neighborhoods again Friday in an operation a local official said was linked to both the airport and subway bombings and to the arrest in the Paris suburbs of a man who may have been plotting a new attack in France.
Speaking after meeting with Belgian Prime Minister Charles Michel, Kerry said the "United States is praying and grieving with you for the loved ones of those cruelly taken from us, including Americans, and for the many who were injured in these despicable attacks."
U.S. Secretary of State John Kerry has arrived in Brussels for counter-terrorism talks with EU and Belgian officials and to pay his respects to the victims of this week's attacks.
A second attacker is suspected of taking part in the bombing this week of a Brussels subway train and may be at large, according to Belgian and French media reports, amid growing signs that the same Islamic State cell was behind the attacks in Brussels and bloodshed in Paris last year.
The Islamic State group has trained at least 400 fighters to target Europe in deadly waves of attacks, deploying interlocking terror cells like the ones that struck Brussels and Paris with orders to choose the time, place and method for maximum chaos, officials have told The Associated Press.
Belgian authorities searched Wednesday for a man pictured at the Brussels airport with two apparent suicide bombers, amid growing suggestions that the bombings of the Brussels airport and subway were the work of the same Islamic State cell that attacked Paris last year.
Presidential candidate Ted Cruz's call for increased surveillance in Muslim neighborhoods following the deadly bombings in Brussels drew sharp rebukes from Muslim Americans and civil rights groups, who panned the Republican's proposal as unconstitutional and counterproductive.
Belgian authorities were searching Wednesday for a top suspect in the country's deadliest attacks in decades, as the European Union's capital awoke under guard and with limited public transport after 34 were killed in bombings on the Brussels airport and a subway station.