By John Irish
DAMMARTIN-EN-GOELE, France (Reuters) - French anti-terrorist police stormed a small printing works in northern France where the two chief suspects in Wednesday's attack on a Paris newspaper had taken hostages, explosions and gunfire ringing out around the building.
The building in the small town of 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. A helicopter hovered overhead.
A third gunman has taken hostages at a Jewish supermarket in Paris demanding the two be allowed to go free.
"At the time of speaking, police forces are in the process, I hope, of apprehending the perpetrators of this act of savagery and making sure they can do no more harm," Prime Minister Manuel Valls said.
No further details of the security forces' late afternoon operation were immediately available.
He was speaking at the offices of the left-wing daily Liberation, temporarily housing what is left of the Charlie Hebdo team, 10 of whom were killed by the Islamist gunmen in an attack on Wednesday. Two police officers were also killed.
Wednesday's Paris attack on the Charlie Hebdo weekly has raised questions about surveillance of radicals, far-right politics, religion and censorship in a land struggling to integrate a five-million Muslim population, the EU's largest.
Security sources said the chief suspects in the attack -- two French-born brothers of Algerian origin under siege now in Dammartin -- were both under surveillance and had been placed on European and U.S. "no-fly" lists.
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!"
(Additional reporting by Paris and U.S. bureaus; Editing by Mark John, Ralph Boulton and Peter Millership)