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Associated Press

PARIS — France fell silent Monday to remember 129 people killed by Islamic State militants as police failed to corner a key escaped accomplice and officials named the alleged Syrian-based mastermind of the attacks, who remained beyond their grasp.

President Francois Hollande led his stunned, jittery nation in one minute's silence at the University of Sorbonne, while thousands more clasped hands outside some of the bullet-riddled nightspots where extremists struck Friday night during a half-dozen attacks that also wounded 350.

Only hours before, Parisians had fled in panic, trampling through memorial candles and messages to the dead, after hearing apparent gunshots that turned out to be fireworks.

But city authorities vowed amid a state of emergency to resume normal life. Children went to school and the Eiffel Tower reopening to tourists after a two-day shutdown. The tower was being floodlit at night in the red, white and blue of the French tricolor along with a projection of Paris' motto of "Tossed but not sunk," suggesting an unsinkable city tossed in the waves.

But as France intensified its air strikes on suspected IS power bases in Syria, police struggled to achieve a breakthrough in their hunt for those linked to France's deadliest attacks since World War II.

In neighboring Belgium, police donning balaclavas and assault rifles mounted a tense hours-long standoff outside the suspected hideout of 26-year-old Salah Abdeslam, who has been identified as the alleged driver of a rental car that delivered attackers to the scene of greatest slaughter, a rock concert inside a nightclub in which 89 died.

That car, rented by Abdeslam, was found abandoned on Paris' east side with several assault rifles and clips of ammunition still inside.

French border police had stopped him Saturday but unwittingly allowed Abdeslam to travel on to Belgium, unaware of an arrest warrant that had been issued in Paris that described him as extremely dangerous.

Police who raided an apartment in the Brussels district of Molenbeek believed to be connected to Abdeslam apparently came up empty Monday after storming the residence, apparently firing tear gas canisters to subdue anyone inside. Police and other Belgian officials said they could not confirm any significant arrests at the scene.

One of Abdeslam's brothers, Brahim, blew himself up outside a Paris restaurant, also killing one civilian, during Friday night's attacks involving six suicide bombers. His other brother, Mohammed, was detained by Belgian police but released without charge Monday. His lawyer Nathalie Gallant said that, unlike his two brothers, Mohammed Abdeslam "didn't make the same life choice" and had not been "tempted into jihadism."

Across France, police utilizing emergency powers said they raided 168 properties and detained 23 people in search of members of a suspected sleeper cell of Islamic State activists. French Interior Minister Bernard Cazeneuve said police seized a Kalashnikov assault rifle and other weapons during the overnight raids.

A French official, who spoke to The Associated Press on condition of anonymity, said police had identified the suspected mastermind as Abdelhamid Abaaoud, a Belgian national believed to operating in Syria. He is featured in a 2014 video apparently taken in Syria boasting of carrying a cargo of killed "infidels" in the back of his vehicle.

The official, who has direct knowledge of the police investigation but is not authorized to speak publicly about the probe, said Abaaoud also is suspected of overseeing two thwarted attacks earlier this year on a Paris church and a Paris-bound train. The latter attack was stopped by American passengers who restrained a gun-toting man before he could open fire.

In hopes of killing Islamic State organizers and trainees, France overnight launched its heaviest airstrikes yet on the city of Raqqa, the group's de-facto capital in Syria. French authorities said Sunday night's bombings destroyed a jihadi training camp and munitions dump.

The Defense Ministry said in a statement that 12 aircraft based in Jordan and the Persian Gulf dropped a total of 20 bombs. It called the operation the largest attack by French air power since France in September joined the U.S.-led coalition in targeting suspected IS power bases in Syria.

Tantalizing clues about the extent of the plot have emerged from Baghdad, where senior Iraqi officials told the AP that France and other countries had been warned Thursday of an imminent attack.

An Iraqi intelligence dispatch warned that Islamic State group leader Abu Bakr al-Baghdadi had ordered his followers to launch gun and bomb attacks immediately and take hostages inside those countries involved in bombing IS positions in Iraq and Syria. The Iraqi dispatch, obtained by the AP, provided no details on when or where the attack would take place.

A senior French security official told the AP that French intelligence services receive such warnings "every day."

However, Iraqi intelligence officials told the AP that they provided specifics to France, including that attackers had been trained specifically for Friday's attack and deployed from Raqqa.

The officials also said a sleeper cell in France met the attackers before their attack and helped them to plan it. They said 24 people were involved: 19 attackers and five who provided logistics and planning.

None of those Iraqi details have been corroborated by officials from France or other Western intelligence agencies. All spoke on condition of anonymity, citing the ongoing investigation.

Harrowing accounts of survival continued to emerge, particularly from the Bataclan theater, where three attackers shot into the fleeing crowd. Two then detonated suicide vests as police stormed the building, fatally shooting the third attacker.

Julien Pearce, a journalist at Europe 1 radio who escaped by crawling onto the Bataclan stage, said he got a good look at one attacker who appeared "very young."

"That's what struck me: his childish face, very determined, cold, calm, frightening," Pearce said.

Paris remains on edge amid three days of official mourning. French troops have deployed by the thousands in support of police to restore a sense of security in one of the most visited cities on Earth. But any sound of loud bangs can sent people scurrying for cover.

Panic ensued Sunday night as police abruptly cleared hundreds of mourners from the Place de la Republique square, where police said firecrackers sparked a false alarm.

"Whoever starts running starts everyone else running," said a city councilwoman, Alice Carton, who was at the square. "It's a very weird atmosphere. The sirens and screaming are a source of fear."

Associated Press reporters Greg Keller, Philippe Sotto, Jamey Keaten, Raphael Satter, Angela Charlton, Jill Lawless, Thomas Adamson and John Leicester in Paris; Raf Casert and John-Thor Dahlburg in Brussels; David Rising in Berlin, Maamoun Youssef in Cairo, Danica Kirka in London and Shawn Pogatchnik in Dublin contributed to this report.