French police officials identified three men as suspects in a deadly attack against newspaper offices that killed 12 people and shook the nation on Wednesday.

Two officials named the suspects as Frenchmen Said Kouachi and Cherif Kouachi, who are brothers and in their early 30s, as well as 18-year-old Hamyd Mourad, whose nationality wasn't immediately clear.

One of the officials said they were linked to a Yemeni terrorist network. A witness of Wednesday's shootings at the offices of weekly satirical newspaper Charlie Hebdo said one of the attackers told onlookers, "You can tell the media that it's al-Qaida in Yemen."

Seven people have been detained in regarding the attack, a judicial source said Thursday.

Confirming earlier comments by Prime Minister Manuel Valls, the source, who refused to be named, said men and women close to the two brothers were currently being questioned by police, without saying where they had been detained.

Valls, meanwhile, told RTL radio that the two suspects -- who are still on the run -- were known to intelligence services and were "no doubt" being followed before Wednesday's attack.

Masked gunmen stormed the offices of Charlie Hebdo methodically killing 12 people, including the editor, before escaping in a car. It was France's deadliest terrorist attack in half a century.

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

During Cherif Kouachi's 2008 trial, he told the court, "I really believed in the idea" of fighting the U.S.-led coalition in Iraq. He said he was motivated by his outrage at television images of torture of Iraqi inmates at the U.S. prison at Abu Ghraib.

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

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