Two brothers suspected of attacking the offices of French satirical newspaper Charlie Hebdo were killed when police stormed their hideout on Friday while their hostage was freed, a police official said.

However, a police source said at least four other hostages had been killed at a separate siege at a kosher supermarket in eastern Paris.

The two brothers died when security forces moved in on a print works in the small town of Dammartin-en-Goele, northeast of Paris, where the chief suspects in Wednesday's attack had been holed up with their hostage.

A police source said the hostage-taker at the Jewish supermarket, who is believed to have had links to the same Islamist group as the brothers, had also been killed.

The print works at Dammartin-en-Goele, set in marsh and woodland, had been under siege since the gunmen abandoned a high-speed car chase and took refuge there early on Friday.

Charlie Hebdo had long courted controversy with satirical attacks on Islam as well as other religions and political leaders. A witness said one of the gunmen in Wednesday's attack was heard to shout: "We have killed Charlie Hebdo! We have avenged the Prophet!"

The gunmen killed 12 people in the attack on the Charlie Hebdo weekly, which raised questions about surveillance of radicals, far-right politics, religion and censorship in a land struggling to integrate part of its five-million Muslim population, the EU's largest.

Security sources said the French-born brothers of Algerian origin had been under surveillance and had been placed on European and US "no-fly" lists. – Reuters