French police are concentrating their search in a rural area of Picardy north-east of Paris where the two men reportedly robbed a petrol station.

For a second night, vigils were held in Paris for the 12 victims of the attack.

In Washington, President Barack Obama signed a book of condolence at the French embassy.

"We go forward together knowing that terror is no match for freedom and ideals we stand for," he wrote, adding: "Vive la France!"

On Friday the Council of Paris is due to hold an extraordinary meeting in which Charlie Hebdo will be made an honorary citizen of the city.

Paris Mayor Anne Hidalgo said it was a rare honour.

"It's also to give strength, to comfort, and to say that these values which were represented by Charlie Hebdo are an integral part of our values," she said.

The attackers are believed to be militant Islamists angered by the satirical magazine's irreverent depictions of the Prophet Muhammad.

Eight journalists, two police officers, a caretaker and a visitor died when two masked men armed with assault rifles burst into the Paris offices. Eleven people were wounded, four of them critically.

Police named the suspects as brothers Cherif and Said Kouachi, born in Paris of Algerian parents.

Two men answering their description robbed a petrol station in Villers-Cotterets, about 80km (50 miles) north-east of Paris on Thursday and the station manager said they were heavily armed with Kalashnikovs and rocket-propelled grenade launchers.

They were last seen driving a Renault Clio car, believed to be the same vehicle they had hijacked in Paris after the attack.

Few details emerged of the search overnight but late on Thursday hundreds of police supported by helicopters were scouring wooded areas in and around the villages of Longpont and Corcy and the town of Villers-Cotterets.

Longpont was sealed off and every house there searched.

French journalist Guillaume Debre told the BBC's Newsday programme that police believe the two suspects had ditched their car and were on foot.

"The big fear for the police is that the two suspects would be able to reach the border with Belgium and would escape the country," he said.

Friday prayers

President Francois Hollande has appealed for tolerance and unity amid fears that underlying social tensions could be worsened by the attacks.

In an unusual move, he invited the leader of the far-right National Front, Marine Le Pen; far-left leader Jean-Luc Melenchon and centrist Francois Bayrou to the Elysee Palace on Friday for talks.With Friday prayers due to be held at mosques across France, Muslim bodies have called on imams to "condemn the violence and the terrorism with maximum firmness".

On Thursday it emerged that the Kouachi brothers were both on the US no-fly list, meaning they were barred from flying into the US.

A senior US official told AFP news agency that one of the brothers was believed to have trained in Yemen with al-Qaeda in the Arabian Peninsula (AQAP).

At least nine people connected to the Kouachi brothers have been detained in the towns of Reims and Charleville-Mezieres, as well as in the Paris area, officials said.

On Thursday, France marked a national day of mourning for the 12 people killed.

A minute's silence was held in public spaces and 20 imams joined hundreds gathered outside the offices of Charlie Hebdo to express sympathy for the victims.

Later, the lights on the Eiffel Tower were turned off.

Several thousand people gathered in the Place de la Republique in Paris for a second night, lighting candles and waving signs that read "Je suis Charlie" ("I am Charlie").

The lawyer for Charlie Hebdo, Richard Malka, has said that next week's edition of the magazine will go ahead on Wednesday and would have a print run of one million, instead of the normal 60,000 copies.

Politicians and journalists across the globe have widely condemned the shooting as an attack on freedom of speech and the press.

(BBC)