Authorities fear a second strike by the suspects, who US counter terrorism officials said were both on the US 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.

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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 US official yesterday said the elder Kouachi had traveled to Yemen, although it was unclear whether he was there to join up with extremist groups like al-Qaeda in the Arabian Peninsula, which is based there.

Witnesses said the attackers claimed allegiance to al-Qaeda in Yemen during the bloody attack Wednesday.

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Both were also on the US no fly list, a senior US counterterrorism official said. The officials spoke on
condition of anonymity because they were not authorized to discuss foreign intelligence publicly.

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 last night in a tribute to the dead from the elegant iron lady that symbolizes France to the world.

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At noon, the Paris Metro came to a standstill and a crowd fell silent near the Notre Dame Cathedral.

The attack struck a chord beyond French borders and similar tributes were held around Europe and elsewhere.

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.

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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.

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