In the aftermath of Morocco's worst-ever terrorist attacks in May 2003, King Mohammed VI lifted the hopes of his most impoverished subjects last year when he toured Casablanca's sprawling slums, home to a dozen suicide bombers who had blasted targets across the city. The monarch said he was appalled at the conditions and vowed to raze the shantytowns, promising new housing for an estimated 150,000 people.

Almost 18 months later, the tin-roofed shacks and squatters' colonies are still here. While a few families have been relocated, the most visible change is a freshly built police station that keeps a closer eye on the slums, part of an ongoing crackdown against alleged Islamic extremists that has resulted in more than 2,100 arrests across the North African nation.

Moroccan government officials tout the arrests and the absence of additional attacks as evidence that they have neutralized the threat of terrorism. But officials in nearby European countries have expressed fears that Morocco, a country with a tradition of Islamic moderation, is becoming more radicalized.

There are numerous signs that Moroccans -- both at home and abroad -- are playing a bigger role in global networks of Islamic militants. In recent months, authorities in Italy, France, Belgium and the Netherlands have broken up apparent terror cells composed primarily of Moroccan immigrants.

In Germany, two Moroccans are facing trial on charges of helping to carry out the Sept. 11, 2001, attacks in the United States, and warrants in the case have been issued for two other people of Moroccan descent. Saudi Arabia's list of most-wanted terrorism suspects also names two Moroccans, the only ones from outside the Arabian Peninsula.

"We cannot exaggerate the threat," said Claude Moniquet, a terrorism researcher and president of the European Strategic Intelligence and Security Center in Brussels. "The terrorist threat in Morocco and the Moroccan community in Europe is real."

In July, Baltasar Garzon, a Spanish magistrate who has handled many of the country's high-profile terrorism cases, said police and intelligence data indicated that 100 al Qaeda cells had taken root in Morocco, calling them "the gravest problem Europe faces today with this kind of terrorism." His comments came as part of the Spanish investigation into the March 11 bombings of four rush-hour commuter trains in Madrid, in which 190 people were killed and more than 1,800 injured. Most of the suspects arrested in the case have been Moroccan immigrants.

Although they are among the largest immigrant groups in Spain, Italy, France and the Netherlands, Moroccans had not attracted much attention from counterterrorism investigators. Muslim radicals from Morocco were not known for embracing violence, unlike those from other North African nations such as Algeria and Egypt.

Those perceptions changed suddenly with the May 2003 attacks in Casablanca, in which 45 people died, including 12 suicide bombers. Since then, the Moroccan government has acknowledged it does not know the whereabouts of about 400 of its citizens who allegedly trained at al Qaeda camps in Afghanistan, Bosnia and Chechnya, some of whom are now thought by the Moroccan authorities to be in Europe.

Moustafa Sahel, the Moroccan interior minister, said the country's security services were slow to detect the growth of radical groups. There was "a long maturation process that we witnessed without reacting," he told Spain's El Pais newspaper in an interview published last month.

He dismissed the idea that Moroccans posed an outsized threat in Europe and suggested that it was xenophobic to single out a particular immigrant group. "Does it mean that Algeria or Saudi Arabia should be accused of exporting terrorists?" he said, noting that Algerian immigrants were responsible for a wave of bombings in France in the 1990s and that 15 of the 19 hijackers in the Sept. 11 attacks in the United States were Saudis.

Seeking a Motive

In Casablanca, however, a tour of slums and other parts of the city suggested that many Moroccans were still struggling to understand what prompted last year's suicide attacks.

In a shantytown known as Carriere Thomas on the outskirts of the city, the mother of one suicide bomber wept quietly and said her son's motives remained a mystery 18 months later.

Abdel Fattah Boulikdane had lived with his mother in the same two-room shack for almost all of his 27 years. He was not overly religious, she said, and had a decent if low-paying job in a shoe factory. On May 16, without even the slightest warning to family or friends, he strapped on a belt of explosives and detonated them at a Spanish cafe on the other side of town.

"I didn't see anything coming," said his mother, Zahra. "It's a situation none of us can understand. How can I judge him when I saw nothing like this coming along?"

The bombers' targets appeared to be Jews and Westerners; in addition to the Spanish cafe, they attacked a Jewish social club, a Jewish cemetery, a Jewish-owned Italian restaurant and a hotel in downtown Casablanca that catered to Westerners.

Moroccan authorities said they were still looking for about a dozen people who are thought to have helped plan the attacks and who recruited the bombers from the slums. Although the plot was allegedly engineered by Moroccans, investigators maintain they were working on behalf of al Qaeda. Moroccan officials cited a February 2003 speech by the al Qaeda leader, Osama bin Laden, in which he warned that Morocco and several other countries would face retribution for helping the United States in its fight against the group.

Repressive Tactics

Morocco has long been one of the most reliable U.S. allies in North Africa and the Islamic world. It was one of the first nations to recognize the United States, formalizing diplomatic relations in 1787. Before his death in 1999, King Hassan II played a key role in U.S. efforts to negotiate peace deals involving Israel.

Since the Sept. 11 hijackings, Morocco's intelligence and security services have cooperated closely with the CIA in tracking and interrogating suspected Islamic militants. The United States, in turn, rewarded Morocco this year with a free-trade agreement.

The alliance is a sore point in some corners of Moroccan society, where there is a running conflict over Western influences. Vandalism is not uncommon at restaurants that serve alcohol or at hotels that cater to foreigners. In 1994, Muslim militants attacked a hotel in Marrakech, killing two Spanish tourists.

Islamic political parties and organizations are also becoming increasingly influential. While King Mohammed VI retains absolute authority and only government-endorsed parties are allowed to field candidates, Islamic movements retain broad public support and have gained power in recent elections. They have also established social welfare programs that in some cases are seen as more effective than those administered by the government.

The mainstream Muslim parties all strongly condemned the May 2003 bombings and espouse nonviolence. But they have clashed with the government over its response to the attacks, criticizing authorities for arresting hundreds of people just because they had ties to Islamic groups and for trying to turn public sentiment against religious parties.

Mustapha Ramid, a leader with the Party for Justice and Development, said government officials used the bombings as a pretext to force 1,000 Islamic candidates to withdraw from local races last year in a bid to weaken his party's growing influence.

He said he and other party officials were forced to step aside to avert a government threat to dissolve the party.

"They had to find a way to make us shut up," he said. "Morocco was on the right track. Since the beginning of the '90s, we were taking the right road toward more freedom and democracy. Since May 16, there is no doubt we have witnessed a regression in this."

Morocco's response to the Casablanca attacks has also drawn increasing scrutiny from international human rights groups. In June, London-based Amnesty International issued a report criticizing the government for "failure to take action on persistent allegations of torture and ill-treatment" in a prison used to detain suspects deemed security risks to the state.

While Amnesty and Human Rights Watch have praised Morocco in the past for ending the practice of capital punishment and instituting other reforms, they have warned that the government is in danger of losing its reputation as a leading progressive light in the Muslim world.

"There are huge pressures on Morocco from the U.S. and from Spain to make security improvements," said Jamil Dakwar, a researcher for Human Rights Watch and co-author of an upcoming report that is critical of the mass arrests. "And that usually means rounding up Islamic radicals, even if they are not the right people."

Mohamed Darif, a professor of law at Hassan II University outside Casablanca and an expert on Islamic militancy, said Morocco has its share of Islamic radicals. But he played down European concerns about a mounting terrorist threat emanating from Morocco, saying that only a few of the radicals embrace violence.

"Terrorism does not exist in our tradition," he said. "It is something coming from abroad. There is no pressure on society in this way. We don't feel constantly insecure that something is going to blow up. You can go to Saudi Arabia or Pakistan and people feel that terrorism is in the air. We don't have this feeling in Morocco."

But Fathallah Arsalan, a spokesman for the banned Justice and Spirituality Islamic movement, said the government passed stricter anti-terrorism laws after the bombings, enabling authorities to detain people without evidence and keep them incommunicado for up to 15 days. Such actions have led to deeper fissures in society, he said.

"With the repression, they are just pushing more and more people to radicalize," Arsalan said. "What can you expect when you put innocent people in jail? What can you expect when you keep people in these conditions? It can only fuel hate and passions."

Staff researcher Robert E. Thomason in Washington contributed to this report.

A series of suicide bomb attacks in Casablanca in May 2003 tore through an Italian restaurant, top left, a Spanish cafe, center, and a Jewish social club, killing 45 people in all in the worst terrorist attacks in Moroccan history. Residents walk through Sidi Moumen, one of Casablanca's sprawling slums where authorities believe several of the May 2003 suicide bombers lived.