French Police Turn Towns Inside-Out in Search for Terrorists at Magazine Office

FLEURY, France— -- French police fanned out across the countryside an hour northeast of Paris on Thursday, carrying out a large-scale operation to hunt down the two brothers suspected in the killings at the offices of Charlie Hebdo on Wednesday.

Men resembling Said and Cherif Kouachi were spotted Thursday morning in the town of Villers-Cotterets, the interior minister said in an evening press conference. Soon after, police were going from village to village in the area around Villers-Cotterets, following up on the reported sighting. A terror alert was expanded from Paris to the Picardie region where the villages are located.

In the small village of Fleury, police tactical teams wearing ski masks and armed with automatic weapons took up positions outside homes as others searched inside. A team from ABC News followed the units - called RAID in France, the equivalent of SWAT in the U.S. – as they slowly, quietly and methodically went down the street from door to door.

Residents appeared at the doors and gates, quietly exchanging information with police as journalists – the only other people on the street – looked on and were repeatedly asked by police to give them space to work.

Just a handful of helicopters roamed the skies while on the ground the tense and dramatic searches – so out of place in such a quaint setting - repeated themselves in villages around the Retz forest. Once a village was cleared, the teams of police would move on, often in convoys of civilian cars with license plates covered with black tape.

Thursday’s operation, while a remarkable show of force, showcased just a small portion of the 88,000 security personnel the interior ministry says has been mobilized across France in the wake of Wednesday’s attack.

Nine people are in custody so far and police have spoken to 90 witnesses, Interior Minister Bernard Cazeneuve said during a news conference today.

The forest is 50 miles east of a town where an apartment was searched Wednesday night, and Crépy-en-Valois, which police sealed off earlier today.

A third suspect, Hamyd Mourad, 18, is cooperating after his surrender in the French town of Charleville-Mezieres, about 140 miles north of Paris, police said.

More than a thousand troops have been deployed on the streets of France as part of the country's heightened state of alert, the French interior minister said today. They will join more than 35,000 gendarmes and paramilitary police -- 10,000 of whom are now protecting the capital. A further 50,000 civil servants from the police and military have also been mobilized as part of France's terror alert -- a total of 88,000 now focused on protecting France after Wednesday's attack, Cazeneuve said in a statement earlier today.

Tensions in Paris remained high today as France began a day of national mourning. A shooting was reported on the city’s southern edge in which at one police officer was shot to death, but it was not immediately clear whether the shooting was linked to the attack on Charlie Hebdo.

Police made several arrests overnight and held people for questioning in Wednesday's attack, Prime Minister Manuel Valls said today. The identities of those being questioned isn't clear, and Said Kouachi and Cherif Kouachi remain on the loose.

The Associated Press contributed to this report. With reporting by ABC NEWS' Dan Good and Meghan Keneally.