A massive police operation, backed by helicopters, is under way northeast of Paris in the search for the main suspects in the deadly attack on satirical magazine Charlie Hebdo.
Officers were searching on January 8 areas near the town of Villers-Cotterets where the two brothers, armed with Kalashnikovs and rocket-propelled grenade launchers, are said to have robbed a gas station.
France has been marking a national day of mourning for the 12 people killed in the January 7 attack on the Paris offices of the weekly magazine -- the worst attack of its kind in France in decades.
The victims included eight journalists and two police officers.
Also on January 8, a gunman killed a policewoman and seriously wounded a second person on the southern edge of Paris.
But officials said there was no evidence of a link between the attack in Montrouge and the Charlie Hebdo killings.
Separately, a source close to the case said investigators found a dozen Molotov cocktails and two jihadist flags in one of the cars used initially in the Charlie Hebdo massacre and which was later abandoned.
Nine people have been detained in the hunt for the suspects -- Cherif Kouachi, 32, who was convicted in 2008 for involvement in a network sending fighters to Iraq, and his brother Said, 34.
The attackers shouted "Allahu akbar" (God is great) and said they wanted to "avenge the prophet" during the attack on the magazine, which had drawn repeated threats for its caricatures of the Prophet Muhammad.
A third man who was initially sought handed himself in to police. It is not yet clear if he is regarded as a suspect.
Prime Minister Manuel Valls voiced concern the attackers could strike again, and authorities are "urgently trying to track down" the culprits.
Interior Minister Bernard Cazeneuve said security had been stepped up across Paris. He mentioned police mobilizations around the headquarters of some media outlets, places of worship, schools, diplomatic representations, and tourist sites.
A minute of silence was observed in public spaces across the country at noon to pay tribute to the victims of the attack, which killed cartoonists whose names were known to millions of citizens and increased tension in a country with a large Muslim population.
A group of imams joined hundreds gathered outside the offices of Charlie Hebdo, which announced it would publish a special edition with a print run of a million copies next week.
The attack sparked strong international condemnation and triggered a wave of demonstrations and expressions of outrage and solidarity with the victims.
On the evening of January 7, tens of thousands of people took part in rallies around France and in other European cities -- including London, Madrid, Amsterdam, New York, and Berlin -- in support of freedom of speech and democracy.
Vigils are continuing across France in the evening of January 8.
But a number of attacks on Muslim targets have been reported in France, with shots fired at two Muslim places of worship. Nobody was hurt in the incidents.
Cazeneuve condemned the attacks, saying he would "not tolerate any act, any threat aimed against a place of worship or any hostile manifestation against French people because of their origin or their religion."
He also said he would host an international meeting in Paris on January 11 with his counterparts from the United States and Europe to discuss the battle against terrorism.
In Britain, the government said it had increased border security, including at ports and checkpoints it operates on French soil in response to the January 7 attack.