U.S. counterterrorism officials are frustrated and angry at Belgium’s inability to tackle ISIS terror cells that are successfully plotting murderous attacks on the West from inside the country’s tiny capital city.

The twin terror attacks in Brussels that left at least 30 dead and 230 injured on Tuesday, despite repeated warnings from Washington, left U.S. officials fuming.

A senior U.S. intelligence officer likened the Belgian security forces to “children.”

“It’s really shitty tradecraft,” the agent told The Daily Beast.

Brussels has become a hotbed of terrorism—concentrated in the Molenbeek district near the city center—and yet the Belgians have made little progress in disrupting a network of violent extremists linked to last year’s Paris attacks that killed 130 people.

Even before the arrest last week in Brussels of Salah Abdeslam, a suspected terrorist behind the Paris attack, there were worries among many U.S. counterterrorism officials of an attack in Belgium. The Belgian authorities had long struggled to resource a counterterrorism campaign. At the same time, it ostracized its burgeoning minority communities, creating isolated enclaves like Molenbeek where potential jihadists could easily hide.

After Abdeslam’s arrest, many in Belgium feared a retaliatory attack. But while U.S. officials sought to help as part of a growing push for U.S. and European cooperation, there were limits, given Belgium’s limited security resources and amid a growing migration community from places like Syria.

News of Tuesday’s attack was met in some parts of Washington with resigned frustration.

“There was only so much we could do to help,” one official explained to The Daily Beast.

“Belgium has been stepping up the amount of people they’re devoting to intelligence and law enforcement but they’re playing catch-up and we’re seeing the terrible results of that today,” Rep. Adam Schiff, the senior Democrat on the House Permanent Select Committee on Intelligence, said on MSNBC.

Indeed, an official said there were warnings as recent as this weekend.

A frustrated U.S. intelligence official bemoaned the state of the counterterrorism apparatus in Belgium and across Europe.

“Even with the EU in general, there’s an infiltration of jihadists that’s been happening for two decades. And now they’re just starting to work on this. When we have to contact these people or send our guys over to talk to them, we’re essentially talking with people who are—I’m just going to put it bluntly—children. They are not pro-active, they don’t know what’s going on. They’re in such denial. It’s such a frightening thing to admit their country is being taken over.”

The end result is that Belgium has been targeted as a base camp for violent extremists.

“Jihadists think that Europe is the soft underbelly of the West and Belgium is the soft underbelly of Europe,” said French terror expert Gilles Kepel.

Many of the major recent attacks in Europe have clear links to Belgium. In May 2014, French ex-Syria jihadist Mehdi Nemmouche went to the Belgian capital to attack the Jewish museum in Brussels. There are Brussels links to the weapons used by Amedy Coulibaly in his attack on a Jewish supermarket on Jan. 9, 2015, shortly after the Jan. 7 attacks on Charlie Hebdo, and the Paris attack in November last year has clear ties to the Molenbeek neighborhood specifically. Many of its attackers either resided or grew up in the borough.

Jean-Charles Brisard, the author of a biography of Abu Musab al-Zarqawi, the founder of ISIS’s earlier incarnation al Qaeda in Iraq, said it’s more useful to think about the ISIS phenomenon in Western Europe as a Francophone network because the operatives in Brussels are a mix of French and Belgian nationals.

Brisard calculates that 534 Belgians have gone to Syria and about 200 have returned; he believes the French-Belgian ISIS apparatus is much greater than European security officials initially thought.

Tracking the individuals is a mammoth task.

“For now, the networks comprise basically 20 individuals around the 10 [Paris] terrorists,” he said. “So it’s least 30. It’s still looking like four or five connected but there might be more that we don’t know yet.” For every terror suspect being surveilled it takes between 20 and 25 counterterrorism officials to track him. Coulibaly, for example, was using 20 different phones, according to Brisard, and each required a different officer to monitor the incoming and outgoing calls.

The Belgians are unwilling or unable to commit that kind of manpower, one of the country’s counterterrorism officials told BuzzFeed a week before the attack.

“Frankly, we don’t have the infrastructure to properly investigate or monitor hundreds of individuals suspected of terror links,” he said.

The problem is exacerbated in Brussels because the local police force is divided into six police corps spread over 19 boroughs (particularly odd since the population is only 1.3 million). Sharing intelligence is complicated by the silos.

Robin Simcox, a British-born specialist on European terror networks who now works at the conservative Heritage Foundation, says the Paris and Brussels attacks prove that European intelligence agencies have been comforting themselves—and their constituencies—with a fallacy for a decade.

“What have they been saying since 7/7?” Simcox asked, referring to the al Qaeda bombings in London in July 2005. “‘Oh, those kinds of attacks are not possible anymore. Any time a network gets too big, we find out about it. Anyone tries to construct a suicide vest, we’ll get it. The attacks will be knives and guns.’ Well, it’s the emperor has no clothes, isn’t it? It happened in Paris, now Brussels; it nearly happened in Verviers back in January [2015]. All kinds of assumptions about the kind of threat we were going to be facing in coming years. And we were all too complacent about it.”

The Belgian field commander, if not quite the “mastermind” of the Paris attacks, Abdelhamid Abaaoud, had previously been linked to four separate terror plots in Europe. He got away each time.

He was thought to have “guided” Nemmouche, the Frenchman who shot up the Jewish museum in Brussels. In the attack planned but later aborted in Verviers, Abaaoud had remotely instructed two Belgian nationals, Sofiane Amghar and Khalid Ben Larbi, who fought with ISIS’s elite Battar Brigade.

Abaaoud had been in Greece at the time, and subsequently returned to Syria after Belgian commandos raided Amghar and Ben Larbi’s safe house in Verviers. (The operation constituted the largest firefight in Belgium since the end of World War II.) Abaaoud was also involved in the failed attack on a high-speed train from Paris to Amsterdam in August 2015. It failed only because three American tourists, two of them in the Oregon National Guard, wrestled the AK-47-wielding gunman to the ground before he could kill anyone.

In a February 2015 issue of ISIS’s propaganda magazine Dabiq, Abaaoud boasts about being able to slip by a continent-wide dragnet for him, despite the fact that European security services all had a recent photograph of him, which had been published by a Western journalist.

“I suddenly saw my picture all over the media, but… the kuffar were blinded by Allah. I was even stopped by an officer who contemplated me so as to compare me to the picture, but he let me go, as he did not see the resemblance! This was nothing but a gift from Allah!”

Abaaoud’s turn from first-generation Belgian into international terrorist follows an all-too-familiar script to those who monitor European jihadism. Although he was once enrolled in the Catholic college Saint-Pierre, an elite school in a tony suburb of Brussels, he dropped out and took to a life of gangsterism and petty crime.

He met Salah Abdeslam and Abdeslam’s brother Brahim (another one of the Paris attackers) when all three were in their late teens or early twenties, hanging about Molenbeek. In 2010, Abaaoud and Salah Abdeslam were convicted of armed robbery after they tried to break into a garage in Ottingnes, a town southeast of Brussels. In 2012, Abaaoud went to jail again for hitting someone in the town of Dendermonde.

Abaaoud apparently radicalized in prison and upon his release, he fell in with a crowd of Islamists, including a veteran of the Afghan jihad against the Soviets in the 1980s, a Moroccan called Khalid Zerkani. The man went by the sobriquet Papa Noel (Santa Claus), owing to his generosity with money: he’d disburse as much as 4,500 euros for aspiring mujahidin seeking to travel to Syria.

Many of those wandering mujahidin have now returned to Brussels; and there is little confidence that the Belgian authorities will be able to stop their murderous plots against the West.