US Secretary of State John Kerry defended Belgium's counterterrorism efforts despite a series of security and intelligence failings in the run-up to the suicide bombings that killed 31 people this week.
Confirming that several FBI agents are involved in the investigation into the attacks, Kerry said the "carping" about Belgium's shortcomings "is a little bit frantic and inappropriate."
Kerry's hastily arranged visit to Brussels today came the day after at least six people were detained in raids linked to Tuesday's attacks on the Brussels airport and subway system. Belgian prosecutors are expected to decide whether to charge or release them, and other raids are reportedly underway today.
Kerry also said the US and other countries had already scheduled meetings with Belgium prior to the attacks about improvements they could make to their laws, intelligence collection and attempts to blunt the radicalisation of youth in particular. The Islamic State group has claimed responsibility for Tuesday's attacks.
"We will not be deterred," Kerry said. "We will come back with greater resolve - with greater strength - and we will not rest until we have eliminated your nihilistic beliefs and cowardice from the face of the Earth."
The international makeup of those killed in Tuesday's attacks was highlighted further today as authorities revealed that American, British, Chinese, French and Dutch citizens were among the dead.
Kerry said Belgium has actively sought additional assistance after the attacks, and that 10 or 11 FBI agents are now in Brussels helping with the investigation. Prime Minister Charles Michel, meeting with Kerry, vowed to step up counterterrorism cooperation with the US and others.
Kerry's comments came as top members of Belgium's embattled government face lawmakers amid heightened criticism of the country's counterterrorism efforts since - and before - last November's Paris attacks, which killed 130 people and which authorities believe were plotted from Belgium.
Some of the Brussels attackers had been on the run from authorities in France and Belgium but were still able to hide in safe houses, assemble bombs and carry out linked attacks. Turkey also announced this week that it had warned Belgium last year that one of the Brussels attackers, Ibrahim El Bakraoui, had been flagged as a "foreign terrorist fighter."
A manhunt is underway for one of the Brussels airport attackers who was recorded on a surveillance video and had fled the scene. Prosecutors have not said how many attackers there were in total, or how many accomplices might be at large.
