BRUSSELS — U.S. 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 on Friday 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 later Friday whether to charge or release them, and other raids are reportedly underway Friday.
Kerry also said the U.S. 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 radicalization 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 Friday 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 U.S. 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.
Belgian prosecutors said the raids Thursday night targeted central Brussels, Jette and the Schaerbeek neighborhood, where police had earlier found a huge stash of explosives and bomb-making material in an apartment used by the Brussels attackers.
French counterterrorism police also detained a man Thursday who officials say was in the advanced stages of an attack plot.
Officials told The Associated Press that the suspect, Reda Kriket, 34, had a past Belgian terrorism conviction and was linked to the suspected ringleader of the Paris attacks, Abdelhamid Abaaoud.
Elsewhere, Belgium's nuclear agency said Friday that it has withdrawn the entry badges of some staff and denied access to other people recently amid concern the country's nuclear plants could be a target for extremists.
Nuclear control agency spokeswoman Nele Scheerlinck said the move at some plants "is not necessarily linked with the terrorist attacks," noting that the decision to deny access usually takes weeks.
Immediately after Tuesday's attacks, security was boosted around Belgium's nuclear sites and hundreds of staff sent home.
Last month, Belgian authorities said searches in the wake of the Paris attacks uncovered video linked to a person working in Belgium's nuclear industry. Belgian media reported this week that Brussels attackers Ibrahim and Khalid El Bakraoui had video recordings of the home of a senior official at the Mol nuclear waste facility in the Flanders region. It's unclear why.
Angela Charlton and John-Thor Dahlburg in Brussels, Lori Hinnant in Paris and Mike Corder in The Hague contributed to this report.