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.
The gunman has threatened to kill the hostages if police storm the terrorist brothers, according to news agency Associated Press.
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.
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.
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