Heavily armed anti-terrorism police swooped on woodland villages northeast of Paristoday in a manhunt for two brothers suspected of being the Islamist gunmen who killed 12 people at a French satirical weekly.
About two dozen helmetted and masked officers carried out house-to-house searches in the village of Corcy, a few km (miles) from a service station where police sources said the brothers were sighted in ski masks. Helicopters flew overhead.
The two fugitive suspects are French-born sons of Algerian-born parents, both in their early 30s, and already under police surveillance. One was jailed for 18 months for trying to travel to Iraq a decade ago to fight as part of an Islamist cell. Officials said they were armed and dangerous.
In Paris, a policewoman was killed in a shootout with a gunman wearing a bulletproof vest. Police sources were unable to say whether that incident was linked to yesterday's assault at the Charlie Hebdo weekly newspaper, but the authorities opened another terrorism investigation.
Bewildered and tearful French people held a national day of mourning, and the bells of Notre Dame pealed for those killed in the attack on Charlie Hebdo, a left-leaning slayer of sacred cows whose cartoonists have been national figures since the Parisian counter-cultural heyday of the 1960s.
The newspaper had been firebombed and hacked in the past for printing cartoons that poked fun at militant Islam and some that mocked the Prophet Muhammad himself. Two of those killed were police posted to protect the paper. One witness described scenes of "carnage".
World leaders described the attack as an assault on democracy. Al Qaeda's Algeria branch praised it, citing a threat by the militant group's founder against those who mock the Prophet Muhammad.
Many European newspapers either re-published Charlie Hebdo cartoons or lampooned the killers with images of their own.
Searches were taking place in Corcy and the nearby village of Longpont, set in thick forest and boggy marshland about 70 km north of Paris.
"We have not found them, there is no siege," an interior ministry official in Paris said. "There were just some witness accounts, so we are checking."
Meanwhile, this morning's shooting of the policewoman on the streets of Paris's southern Montrouge district - whether related or not - set the country even further on edge.
Montrouge Mayor Jean-Loup Metton said the policewoman and a colleague were responding to a traffic accident when the shooting broke out. Witnesses said the assailant fled in a Renault Clio and police sources said he wore a bullet-proof vest and had a handgun and an assault rifle.
One police officer at the scene told Reuters he did not appear to resemble the Charlie Hebdo shooter suspects.
Prime Minister Manuel Valls was asked on RTL radio after an emergency cabinet meeting with President Francois Hollande whether he feared a further attack.
"That's obviously our main concern, and that is why thousands of police and investigators have been mobilised to catch these individuals."
"ARMED AND DANGEROUS"
Police released photographs of the two suspects, Cherif and Said Kouachi, 32 and 34. The brothers were born in eastern Paris to Algerian parents who died when they were still children. They grew up in an orphanage in the western city of Rennes.
The younger brother's jail sentence for trying to fight in Iraq a decade ago, and more recent tangles with the authorities over suspected involvement in militant plots, raised questions over whether police could have done more to watch them.
Cherif Kouachi was arrested on Jan. 25, 2005 as he was preparing to fly himself to Syria en route to Iraq, and served 18 months of a three-year sentence.
"He was part of a group of young people who were a little lost, confused, not really fanatics in the proper sense of the word," lawyer Vincent Ollivier, who represented Cherif in the case, told Liberation daily. "He hadn't really given any great thought to Islam and didn't seem all that determined."
In 2010 he was suspected of being part of a group that tried to free from prison Smain Ali Belkacem, a militant jailed for the 1995 bombings of Paris train and metro stations that killed eight people and wounded 120. That case against Cherif Kouachi was dismissed for lack of evidence.
Video footage of the attack suggested there may have been only two gunmen, who drove off from the scene in a black car.
A third person wanted by police, an 18-year-old man, turned himself into police in Charleville-Mézières near the Belgian border late on Wednesday. A legal source said he was the brother-in-law of one of the brothers. French media quoted friends as saying he was in school at the moment of the attack.
In the wake of the attack that rocked France, authorities tightened security at transport hubs, religious sites, media offices and stores.
During the morning, there were scattered, unconfirmed reports of sightings of the assailants and police increased their presence at entry points to Paris.
One police source talked of a type of "psychosis" setting in with various reports and rumours, but police had to take each of them seriously.
The defence ministry said it sent 200 extra soldiers from parachute regiments across the country to Paris to take the number of military patrolling the capital's streets to 850.
Tens of thousands took part in vigils across France on Wednesday to defend freedom of speech, many wearing badges declaring "Je suis Charlie" in support of the newspaper and the principle of freedom of speech.
Many German newspapers republished Charlie Hebdo cartoons.
Britain's Daily Telegraph depicted two masked gunmen outside the doors of Charlie Hebdo saying to each other: "Be careful, they might have pens."
Charlie Hebdo's lawyer Richard Malka said the newspaper would be published next Wednesday with one million copies compared to its usual print run of 60,000.
The attack raised questions of security in countries across the Western world and beyond. Muslim leaders condemned the shooting but some have expressed fears of a rise in anti-Islamic feeling in a country with a large Muslim population.
France's Muslim Council called on all French Muslims to join the minute of silence and said it was issuing a call for "all Imams in all of France's mosques to condemn violence and terrorism wherever it comes from in the strongest possible way."
Police sources said the window of a kebab shop next to a mosque in the town of Villefrance-sur-Saone was blown out by an overnight explosion. Local media said no one was hurt.