The attack has raised questions in France about policing, surveillance of radicals, far-right politics, religion and censorship - all in a country still struggling to integrate its five-million-head Muslim population, the EU's largest.
On Friday, police vans, armoured cars and ambulances ringed the town of Dammartin-en-Goele, set in marsh and woodland, and helicopters hovered overhead. Residents were told to stay at home and schools near a printing works where two gunmen were holed up were evacuated.
A second hostage-taking was reported at a Paris kosher supermarket. French media said at least two had been killed in a shoot-out there, but police said they could not confirm any deaths.
The Interior Ministry said security forces surrounding a small print works in Dammartin-en-Goele were trying to make contact with the gunmen, who had earlier in the day evaded police in a high-speed car chase on a highway to Paris.
"This can take a long time, hours and sometimes days," Interior Minister spokesman Pierre-Henry Brandet said in a tweet.
Yves Albarello, local MP for the Seine-et-Marne department and member of the crisis cell put in place by authorities, told iTELE the two suspects had let it be known that they wanted to die "as martyrs".
The gunmen had been on the run since they stormed the Paris offices of Charlie Hebdo, a satirical journal known for its ridicule of Islam and other religions as well as political figures. Western leaders condemned the attack as an assault on democracy. Al Qaeda's North Africa branch praised the gunmen as "knight(s) of truth".
A senior Yemeni intelligence source told Reuters one of the two suspects was in Yemen for several months in 2011 for religious studies; but there was no confirmed information whether he was trained by Al Qaeda in the Arabian Peninsula (AQAP).
News of a further shootout, in Paris, a third in two days, demonstrated the scale of the threat facing French authorities and the force of nearly 90,000 mobilised nationwide for the search action.
A police source said several people were taken hostage at a kosher supermarket in eastern Paris after a shootout involving a man armed with two guns.
The source said he bore a resemblance to the gunman suspected of killing a policewoman in a separate shooting in southern Paris on Thursday and believed to be a member of the same jihadist group, Butte Chaumont, as the two Hebdo suspects.

Police released pictures of a 32-year-old man, Amedy Coulibaly, and a 26-year-old woman, Hayat Boumeddiene, wanted in connection with the southern Paris incident.
The prospect of multiple attacks is one that has troubled Western security services since Islamist militants hit a number of targets in Mumbai in 2008, killing 166 people.
Yohann Bardoux, a plumber whose office is two doors down from the printing shop where the hostage-taking was playing out  stayed away from work after hearing gunfire. But he said his mother was in the building next door to the printing shop.
"Of course I'm worried about her, I hope it all comes down soon, and turns out well," Bardoux said.
"They are everywhere. It's really jumping. They've blocked the whole zone, we've got helicopters overhead, the police presence is impressive."
A spokesman for Charles-de-Gaulle airport said all its runways were open but that landings were only taking place at the two south terminals.

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