Belgium was left reeling after three attacks left at least 31 people dead and more than 200 injured March 22. The terror began unfolding during peak rush hour, and ended with at least one suspect still at large. (Deirdra O'Regan/The Washington Post)

The investigation into last week’s bombings in Brussels extended farther across Europe on Sunday, after Italian police arrested a new suspect thought to have provided false documents to the Islamic State militants behind recent attacks here and in Paris.

The latest arrest adds to an emerging picture of the network that staged some of the worst attacks on European soil since World War II, another striking indication of the reach of the Islamic State beyond its strongholds in Iraq and Syria.

Fears remained heightened across the continent nearly a week after suicide bombers killed at least 31 people at Brussels Airport and, an hour later, in a crowded subway car. Tuesday’s assaults shed new light not only on the shortcomings of European security agencies but also on the militants’ determination to launch attacks.

In St. Peter’s Square in Vatican City, worshipers were subject to tight security Sunday as they flocked to hear Pope Francis deliver his Easter address. Speaking to the crowd, the pope called terrorism a “blind and brutal form of violence,” according to the Associated Press.

In central Brussels, widespread anxiety was visible as riot police with shields and white helmets fanned out Sunday afternoon around a memorial site for victims. Police briefly fired water cannons after several hundred men dressed in black, apparently soccer fans, advanced into the area. The fans waved a giant banner against the Islamic State and, according to some media reports, shouted nationalist slogans.

What we know about the connections between the Brussels and Paris attacks

One of the participants, who identified himself only as Steve, said the fans were not protesting against immigrants or Muslims. He said they had hoped only to show their condemnation of terrorists and of government failures to deal with such threats.

“We are people who are just united against the [expletive] happening to this country,” he said by phone later in the day.

Government officials urged organizers to postpone a solidarity rally planned for Sunday, saying that police could not provide adequate security.

Belgian authorities, meanwhile, expanded their hunt for new clues. They conducted 13 searches in Brussels and other areas Sunday, the federal prosecutor’s office said. Four people detained in those searches remain in custody.

Prosecutors also charged another suspect linked to the attacks, local media reported Sunday. The man, identified by authorities only as Abderrahmane A., has been in custody since Friday and faces charges of belonging to a terrorist organization. Belgian police did not provide details.

The man captured by Italian authorities Saturday was an ­Algerian suspected of providing several Islamic State supporters with false identification documents, allowing them to evade authorities while plotting attacks in Belgium and France.

Belgian authorities have released more details about the suspects linked to the deadly terror attacks in Brussels. (Claritza Jimenez/The Washington Post)

“The Algerian arrested today in Salerno is part of a network of forgers of residency” documents, police said in a message Saturday on Twitter.

According to the Italian news agency ANSA, 40-year-old Djamal Eddine Ouali had been the subject of a Belgian arrest warrant since January. ANSA said he was suspected of having given falsified papers to Salah Abdeslam, a suspected member of the cell that carried out the Nov. 13 Paris attacks who is now in Belgian custody. Ouali is also believed to have furnished documents to Najim Laachraoui, suspected to have been one of the suicide bombers at Brussels Airport, and to a man killed by Belgian authorities in a raid this month before the attacks.

The new steps in the investigation come as Belgian authorities seek to beat back criticism of their handling of terrorism threats.

Investigators acknowledged late last week that they did not question Abdeslam extensively after his March 18 arrest, possibly missing clues that might have helped them avert the attacks four days later.

On Sunday, Interior Minister Jan Jambon defended to local media the government’s decision-making during last week’s attacks. He has come under fire for failing to protect other Brussels residents after the initial attack at the airport.

That criticism made the weekend announcement that authorities may have captured the most-wanted remaining suspect from Tuesday’s attacks even more welcome news.

According to a European security official, the man is Fayçal Cheffou, whose is suspected to be the third attacker at Brussels Airport. His explosives-laden suitcase apparently did not detonate.

The man, whom Belgian officials have not fully identified, was charged Saturday with “participation in the activities of a terrorist group, terrorist murders and attempted terrorist murders.”

According to Belgian media, Cheffou has described himself as a journalist in the past and has promoted radical Islamist beliefs.

Belgian authorities also have charged a man identified as ­“Rabah N.” with taking part in a terrorist group and another man, identified as “Aboubakar A.,” with a terrorism-related offense.

The latest person to be charged may be Abderrahmane Ameroud, whom Belgian media has reported as linked to the attacks. Ameroud was sentenced by a French court to seven years in prison for involvement in a plot to assassinate Ahmed Shah Massoud, a legendary Afghan guerrilla leader. Massoud was killed in 2001.

It is not known what exactly each person is suspected to have done.

Over the weekend, militants continued to celebrate attacks that they said demonstrated the weakness of Western defenses. In a video released Saturday, a Dutch-speaking fighter, identified as Abu Hanifa al-Beljiki, addressed the government of Belgium.

“You learned nothing from the lessons of Paris, because you continued fighting Islam and the Muslims,” he said, according to a transcript from the SITE Intelligence Group. “For this I want to tell you that the attack in Brussels is reaping what you had sown with your own hands.”

More than 300 people were wounded in the attacks, Belgian officials have said. Nearly half of the victims were foreign nationals, including at least four Americans. According to Belgium’s Foreign Ministry, not all of those wounded have been identified because some of them remain comatose.

Annabell Van den Berghe contributed to this report.

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