PARIS — Police SWAT teams backed by helicopters tracked two heavily armed brothers with al-Qaida sympathies suspected in the newsroom massacre of a satirical French weekly that spoofed Islam, honing in Thursday on a region north of Paris as the nation mourned the dozen slain.
Authorities fear a second strike by the suspects, who U.S. counterterrorism officials said were both on the U.S. no-fly list, and distributed their portraits with the notice "armed and dangerous." More than 88,000 security forces were deployed on the streets of France.
They also extended France's maximum terror alert from Paris to the northern Picardie region, focusing on several towns that might be possible safe havens for the two — Cherif Kouachi, 32, and Said Kouachi, 34.
A senior U.S. official said Thursday the elder Kouachi had traveled to Yemen, although it was unclear whether he was there to work with extremist groups like al-Qaida in the Arabian Peninsula, which is based there. Witnesses said the attackers claimed allegiance to al-Qaida in Yemen during the bloody attack Wednesday.
A French security official said American authorities had shared intelligence indicating that Said Kouachi had traveled to Yemen several years ago for training and French authorities were seeking to verify the accuracy of the intelligence. The official spoke on condition of anonymity because of the sensitivity of the matter.
The worst spasm of terror violence in more than a half-century stunned France. The lights of the Eiffel Tower went out Thursday night in a tribute to the dead from the elegant iron lady that symbolizes France to the world. At noon, the Paris Metro came to a standstill and a crowd fell silent near the Notre Dame Cathedral.
French President Francois Hollande — joined by residents, tourists and Muslim leaders — called for tolerance after the country's worst terrorist attack in decades.
"France has been struck directly in the heart of its capital, in a place where the spirit of liberty — and thus of resistance — breathed freely," Hollande said.
Nine people, members of the brothers' entourage, have been detained for questioning in several regions. In all, 90 people, many of them witnesses to the grisly assault on the satirical weekly Charlie Hebdo, were questioned for information on the attackers, Interior Minister Bernard Cazeneuve said in a statement.
The minister confirmed reports the men were identified by the elder brother's ID card, left in an abandoned getaway car, a slip that contrasted with the seeming professionalism of the attack.
A third suspect, 18-year-old Mourad Hamyd, surrendered at a police station Wednesday evening after hearing his name linked to the attacks. His relationship to the Kouachi brothers was unclear.
The Kouachi brothers — the Paris-born offspring of Algerian parents — were well known to French counterterrorism authorities. Cherif Kouachi, a former pizza deliveryman, had appeared in a 2005 French TV documentary on Islamic extremism and was sentenced to 18 months in prison in 2008 for trying to join up with fighters battling in Iraq.
Eight journalists, two police officers, a maintenance worker and a visitor were killed in the attack and 11 people were wounded, four of them critically. The publication had long drawn threats for its depictions of Islam, although it also satirized other religions and political figures.
Charlie Hebdo had caricatured the Prophet Muhammad, and a caricature of Islamic State's leader was the last tweet sent out by the irreverent newspaper, minutes before the attack. Its feed has since gone silent.
Charlie Hebdo planned a special edition next week, housed in the offices of another paper.
"The paper will continue because they haven't won," Patrick Pelloux, a Charlie Hebdo columnist said tearfully to iTele TV.
Editor Stephane Charbonnier, known as Charb, who was among those slain, "symbolized secularism ... the combat against fundamentalism," his companion, Jeannette Bougrab, said on BFM-TV.
"He was ready to die for his ideas," she said.
Witnesses to the massacre have said the attackers claimed allegiance to al-Qaida in Yemen, and on videos they were heard saying they were avenging the prophet. "Tell the media that it's al-Qaida in Yemen," the two shouted as they were fleeing, one witness, Cedric Le Bechec, wrote on Facebook.
The governor of a southern province in Yemen told The Associated Press on Thursday that four French citizens had been deported from Yemen in the last four months. Gov. Ahmed Abdullah al-Majidi said he didn't have their names and there was no confirmed link between those deportations and the Charlie Hebdo attack.
Jarring France further, two mosques in France were firebombed Thursday and a police officer was killed in Montrouge, on the southern edge of Paris. However, Cazeneuve told reporters there was no known link between that killing and the attack on Charlie Hebdo.
Police searched apartment in Reims, in the Champagne region, where the interior minister said Said Kouachi lived, with technicians gathering samples.
The hunt moved further north after a report that two men resembling the suspects robbed a gas station in Villers-Cotterets early Thursday. The focus then enlarged to Crepy-en-Valois, where heavily armed security forces with air cover and a giant black rapid intervention truck moved through rural streets and among old stone buildings.
Authorities around Europe have warned of the threat posed by the return of Western jihadis trained in warfare. France counts at least 1,200 citizens in the war zone, headed there, returned or dead, and officials have said France is a preferred target. Both the Islamic State group and al-Qaida have issued threats to France — home to Western Europe's largest Muslim population.
France is taking part in airstrikes in Iraq in a bid to defeat the Islamic State group, and intervened to rout out al-Qaida extremists from northern Mali, a former French colony.
The French suspect in a deadly 2014 attack on a Jewish museum in Belgium had returned from fighting with extremists in Syria; and the man who rampaged in southern France in 2012, killing three soldiers and four people at a Jewish school in Toulouse, received paramilitary training in Pakistan.
A journalist who took refuge on the building roof during the attack said that when he went into Charlie Hebdo's offices he was confronted with life and death.
"On the one side the living and the other the dead," Edouard Periin told iTele. The dead and dying, he said, were on the left.
Associated Press writers Sylvie Corbet in Paris; Ahmed Al-Haj in Sanaa, Yemen; Chris van den Hond in Crepy-en-Valois; and Michel Spingler in Villers-Cotterets contributed to this report.