THE youngest of the three suspects being hunted after the killing of 12 people in Paris handed himself in in the early hours of this morning, according to reports in France.

Police have made another six arrests, believed to be associates or relatives of the suspects.

Three men were identified as suspects in the attack against the French newspaper offices that shook the nation.

Police officials named the suspects as Frenchmen Said Kouachi and Cherif Kouachi, in their early 30s, as well as 18-year-old Hamyd Mourad.

According to French media reports, Mourad surrendered to police after his name began circulating on social media.

Officials said the suspects were linked to a Yemeni terrorist network.

Cherif Kouachi was convicted in 2008 of terrorism charges for helping funnel fighters to Iraq's insurgency and sentenced to 18 months in prison.

It was the deadliest attack in France in half a century.

Masked gunmen stormed the offices of the satirical newspaper Charlie Hebdo, that caricatured the Prophet Muhammad.

They methodically killed 12 people, including the editor, before escaping in a car.

Shouting "Allahu akbar!" as they fired, the men claimed links to al Qaida in their military-style, noon-time attack on the weekly paper, located near Paris' Bastille monument.

The publication's depictions of Islam and Islamic extremists have drawn condemnation and threats before - it was firebombed in 2011 - although it also satirised other religions and political figures.

Both al Qaida and the Islamic State group (IS) have repeatedly threatened to attack France, which is conducting airstrikes against extremists in Iraq and fighting Islamic militants in Africa.

President Francois Hollande said it was a terrorist act "of exceptional barbarism," adding that other attacks have been thwarted in France in recent weeks.

Fears have been running high in France and elsewhere in Europe that jihadis returning from conflicts in Syria and Iraq will stage attacks at home.

In a sombre address to the nation tonight, Mr Hollande pledged to hunt down the killers, and pleaded with his compatriots to come together in a time of insecurity and suspicion.

"Let us unite, and we will win," he said. "Vive la France!"

France raised its security alert to the highest level and reinforced protective measures at houses of worship, stores, media offices and transportation.