Paris: Two brothers suspected of having gunned down 12 people in an Islamist attack on satirical magazine Charlie Hebdo were spotted this morning and are armed, sources close to the manhunt said.

The manager of a petrol station near Villers-Cotteret in the northern Aisne region "recognised the two men suspected of having participated in the attack against Charlie Hebdo", the source said.

Two men resembling the suspects robbed a gas station in northeast France this morning and police swarmed the site while helicopters hovered above. Officials said later the newspaper attackers were not there.

This combo shows handout photos released by French Police in Paris early on January 8, 2015 of suspects Cherif Kouachi (L), aged 32, and his brother Said Kouachi (R), aged 34, wanted in connection with an attack at the satirical weekly Charlie Hebdo in the French capital that killed at least 12 people. Pic/AFP/French Police

French Prime Minister Manuel Valls said the two suspects still at large in the Charlie Hebdo slayings, Cherif Kouachi, 32, and Said Kouachi, 34, were known to France's intelligence services.

Cherif Kouachi was convicted of terrorism in 2008 for being involved in a network sending radical fighters to Iraq. The two should be considered "armed and dangerous," French police said in a bulletin, appealing for witnesses after a fruitless search in the city of Reims, in French Champagne country.

A third suspect, Mourad Hamyd, 18, surrendered at an eastern police station after learning his name was being linked to the attacks in the news, said the Paris prosecutor spokeswoman Agnes Thibault-Lecuivre. She did not specify his relationship to the Kouachi brothers.

A French security official said seven people had been arrested overnight, speaking on condition of anonymity because the investigation was ongoing. He did not elaborate on their possible links to terror.

One police official, speaking on condition of anonymity because the investigation was ongoing, said the suspects were linked to a Yemeni terrorist network. Both al-Qaeda and the Islamic State group have repeatedly threatened to attack France, which is conducting airstrikes against extremists in Iraq and fighting Islamic militants in Africa.

Cherif Kouachi, who was sentenced to 18 months in prison after being convicted of terrorism charges in 2008, has said he was outraged at the torture of Iraqi inmates at the US prison at Abu Ghraib near Baghdad.