PARIS — Police in France and Belgium staged more than 160 anti-terrorism raids on Monday as authorities expanded crackdowns, seized weapons and cast their nets wider for suspects in the Paris attacks.
The intense manhunts unfolded as clearer portraits emerged of the network behind Friday’s carnage that left at least 129 people dead and more than 350 wounded. Among the possible central figures is a Belgian militant, now apparently in Syria, who also could have links to a foiled assault aboard a high-speed Paris-bound train in August.
Another suspect atop the wanted list is a French man who may have slipped away as seven other assailants died in the waves of suicide blasts and gunfire.
Also coming into sharper relief: Indications that more of the alleged plotters were known to European investigators long before the massacres.
At the same time, authorities dug deeper into an apparent nexus between Islamic State strongholds in Syria and militant cells in Europe — in particular a Brussels district that is home to many with roots in North Africa and elsewhere.
In the city’s Molenbeek neighborhood, police sealed off streets during sweeps of homes and apartment blocks, arresting at least one person. But Belgian officials did not announce that any pivotal suspects were in custody.
In France, where nearly two dozen people were arrested, the nation observed a moment of silence. The Eiffel Tower, which dimmed its lights in mourning, was planned to be relit at sundown in the national colors of red, white and blue.
Even as Europe and allies marshaled its forces after the attacks — including stepped-up airstrikes by France in Syria — a purported Islamic State-backed video threatened more strikes in cities including Washington.
The six-minute Arabic-language video released by an Islamic State-linked group in Iraq appears to show militants in Iraq praising the Paris shootings and warning that one day the militants “will strike America in its heartland, in Washington . . . we will invade Rome,” according to a translation by the SITE Intelligence Group, which monitors militant Web sites.
The authenticity of the video — released on a social media site believed linked to the Islamic State — could not immediately be confirmed. But it lacks some of the hallmarks of previous Islamic State videos, such as dramatic music, slow-motion shots and polished production values.
As investigators followed dozens of leads, many appeared to intersect in Molenbeek in Brussels. Those whose names are emerging include Belgian national Abdelhamid Abaaoud, a 27-year-old son of Moroccan immigrants and raised in Molenbeek.
Abaaoud, a graduate of one of Brussels’s most prestigious high schools, appeared to move higher in the Islamic State ranks over the years and made no secret of his intentions to strike in Europe, the Associated Press reported.
In February, Abaaoud was quoted by the Islamic State’s online magazine, Dabiq, as saying he fled to Syria after Belgian authorities broke up an alleged terror cell in the eastern city of Verviers the previous month. At the time, Abaaoud was named as a suspect, the magazine said.
French officials also told the AP that Abaaoud is believed to have ties to other thwarted attacks, including one by a gunman who opened fire on an Amsterdam-to-Paris train in August but was subdued by three American travelers. The gunman, a 26-year-old Moroccan, was arrested.
Meanwhile, another top suspect was sought: an assailant who could have slipped away in the chaos after the gunfire and bombings Friday night in Paris.
French police initially said that eight assailants took part in the Paris attacks in three groups — with seven dying amid the bloodshed. The possibility that an eighth attacker was still at large raised hope he could be captured alive and provide critical information on how the attacks took shape and were funded and directed.
French police on Sunday issued an urgent alert and released a photo of a suspect: Salah Abdeslam, a Belgian-born French national. Meanwhile, authorities have sketched out the possibility of a larger network linked to the Islamic State that could involve as many as 20 plotters with links stretching to war-ravaged Syria.
French Prime Minister Manuel Valls said authorities were using the country’s state of emergency to search and question possible terrorist suspects throughout France as part of a “war” on militants.
“Let this be clear to everyone,” said Interior Minister Bernard Cazeneuve. “This is just the beginning, these actions are going to continue.”
He said at least 23 people were detained in overnight raids — at least three near the southern city of Toulouse and several near Lyon — and weapons were seized, including a rocket launcher and automatic rifles.
An earlier death toll of 132 was reduced to 129 after medical officials said they doubled counted some of Friday’s victims.
Authorities also identified two more of the attackers, one of them a 28-year-old Frenchman already charged in a terrorism investigation in 2012.
Samy Amimour, who blew himself up at the Bataclan music hall Friday night, the site of the deadliest attack, had been placed under judicial supervision. An international arrest warrant was issued in the fall of 2013 after he failed to comply with bail conditions. Three of his relatives were placed under police custody Monday morning.
The other new name released Monday was that of Ahmad al-Mohammed, who blew himself up outside the national soccer stadium. He was found with a Syrian passport that gave his name as Ahmad Almohammad, a 25-year-old born in Idlib. The prosecutor’s office says fingerprints from the attacker match those of someone who passed through Greece in early October.
Valls, the French prime minister, said the attack was “organized, conceived and planned” from Syria, where a nearly five-year-old civil war is raging. Waves of migrants fleeing the civil war have fled to Europe, raising worries that militants could also have used the exodus as way into the continent.
“Clearly there was an effort that was underway for quite some time,” said CIA Director John Brennan, speaking at a conference in Washington. He said the ability of European security agencies to “monitor and surveil these individuals is under strain.”
President Obama, speaking at a G-20 conference in Turkey, called the Paris bloodshed “a terrible and sickening” spectacle in what he predicted would be a long fight against the Islamic State. But he clearly ruled out deploying large-scale U.S. ground troops against the Islamic State in its Syrian bases, insisting that air attacks and other current strategies were the best way to eventually defeat the group.
On Wednesday, President François Hollande will present a bill to the National Assembly calling for a three-month state of emergency — a move granting exceptional police powers to restrict freedom of movement and gatherings at public places.
Yet Europeans and their governments were confronting a chilling reality at home. A rogues’ gallery of homegrown terrorists with links to Islamist groups has become large enough — and is acting stealthily enough — to make tracking them increasingly difficult for the region’s intelligence agencies.
At least two of the eight known attackers had spent time in Syria, according to two European intelligence officials, who like many interviewed for this article spoke on the condition of anonymity to discuss the ongoing investigation.
One of them, Bilal Hadfi, a 20-year-old French national, was known to have returned from the Middle East to Belgium. He then disappeared from the radar of the Belgian security services.
Another attacker, 29-year-old French national Ismael Omar Mostefai, was mentioned twice in warnings from Turkey in the past year saying he had likely crossed into Syria, a senior Turkish official said, speaking on condition of anonymity because of he was not authorized to speak to news media.
Turkish officials said they notified France in December 2014 and then again in June that Mostefai had entered Turkey in 2013 and that there was no record of his having exited the country, the official said. There was no apparent response from France, the official said.
In 2010, Mostefai first came to the attention of French intelligence because of his association with radical Islamists at a mosque in Lucé, near Chartres, a city southwest of Paris.
Mostefai is thought to have traveled to Syria in the winter of 2013, a French police official familiar with the case said. “That is when we lost track of him,” the official said.
Deane reported from London, Murphy from Washington. Cléophée Demoustier, Virgile Demoustier, Karla Adam and Monique El-Faizy in Paris, Steven Mufson in Brussels, Liz Sly in Baghdad, Hugh Naylor in Beirut, Greg Miller in Washington and Elinda Labropoulou in Athens contributed to this report.