PARIS -- The two French brothers wanted in the newspaper-office bloodbath in Paris were already known to U.S. counterterrorism authorities and had been put on the American no-fly list, a senior U.S. official said Thursday.

Another U.S. official said the older brother, Said Kouachi, had travelled to Yemen. It was unclear whether he was there to join up with extremist groups like Al Qaeda.

Witnesses said the gunmen who carried out Wednesday's shooting rampage claimed allegiance to al Qaeda's offshoot in Yemen.

The details emerged as French authorities conducted an all-out manhunt for the Kouachi brothers -- Cherif, 32, and Said, 34 -- in the attack that killed 12 people at the offices of Charlie Hebdo, a weekly that lampooned radical Islam and the Prophet Muhammad.

They were identified as suspects after the older brother's ID card was found in the getaway car, authorities said.

Both men -- the Paris-born offspring of Algerian parents -- were already known to French counterterrorism authorities.

Cherif, a former pizza deliveryman, had appeared in a 2005 French TV documentary on Islamic extremism and was sentenced to 18 months in prison in 2008 for trying to join up with fighters battling in Iraq.

U.S. officials would not say if the Kouachis were believed to have fought in the Middle East with extremist groups.

It would not be unusual for known extremists to be placed on the U.S. no-fly list.

A French security official, speaking on condition of anonymity because of the sensitivity of the matter, said that American authorities had shared intelligence with France indicating that Said had travelled to Yemen several years ago for training, and were seeking to verify its accuracy.

Before the words of a radical preacher persuaded him to book a flight to Syria to wage holy war, Cherif Kouachi was a ladies' man who belted out rap lyrics.

It was the teachings of a firebrand Muslim preacher that put him on the path to jihad in his rough-and-tumble neighbourhood of northeastern Paris, Kouachi was quoted as saying in the documentary.

The cleric "told me that (holy) texts prove the benefits of suicide attacks," Kouachi was quoted as saying. "It's written in the texts that it's good to die as a martyr."

Associated Press reporters who covered his 2008 trial, which exposed a recruiting pipeline for Muslim holy war in the multi-ethnic and working-class 19th arrondissement of Paris, recalled a skinny young defendant who appeared very nervous in court.

Cherif Kouachi's lawyer said at the time that his client had fallen in with the wrong crowd.

During the trial, Kouachi was said to have undergone only minimal training for combat -- going jogging in a Paris park to shape up and learning how a Kalashnikov automatic rifle works by studying a sketch.

He was described at the time as a reluctant holy warrior, relieved to have been stopped by French counterespionage officials from taking a Syria-bound flight that was ultimately supposed to lead him to the battlefields of Iraq.

French Interior Minister Bernard Cazeneuve, however, said Thursday that Kouachi had been described by fellow would-be jihadis at the time as "violently anti-Semitic."

Imprisonment changed him, his former attorney Vincent Ollivier told Le Parisien newspaper in a story published Thursday.

Kouachi became closed off and unresponsive and started growing a beard, the lawyer said, adding that he wondered whether the stint behind bars transformed his client into a ticking time bomb.

There was a time, though, when he had very different interests.

Footage in the documentary, part of a prestigious French public television series titled "Evidence for the Prosecution," shows him in 2004, when, according to the narrator, the lanky young man in a black T-shirt with extremely close-cropped hair and a chunky wristwatch was keener on spending time with pretty girls than on going to the mosque. He appears relaxed and smiling as he pals around with friends.

At one point, with his baseball cap worn backward, Kouachi belts out some rap music and breaks into a joyful dance.

After he was released from prison, he worked in a supermarket's fish section in the Paris suburbs for six months beginning in 2009. Supervisors said he gave no cause for concern.

In 2010, police detained him again in a probe of an alleged plot to free an Islamic militant sentenced to life in prison for bombing a Paris train line in 1995. Kouachi was ultimately released with no charges ever brought.

Much less has become public about Said, but Cazeneuve said the jobless resident of the city of Reims was also known to authorities, despite having never been prosecuted, because he was "on the periphery" of the illegal activities his younger sibling was involved in.

In Reims, about 90 miles (145 kilometres) northeast of Paris,) Said frequented a prayer room on the ground floor of an apartment building, according to the local imam, Abdul-Hamid al-Khalifa.

Al-Khalifa told the AP that Said wore traditional North Africa clothes to prayers and didn't mix much -- if at all -- with other worshippers.

"Typically, he'd come late to prayers and leave right when they were done," Al-Khalifa said in a telephone interview.

If French authorities are now hunting for the right suspects, it may be because of Said, Cazeneuve hinted.

In the stolen Citroen abandoned Wednesday by the gunmen, police found a French identity card in the older Kouachi's name, the minister said.

Moreover, after the attackers dumped the first car, they grabbed another, and Cazeneuve said the elder Kouachi had been identified as "the aggressor" by witnesses shown his photo.

A third suspect identified by French authorities in the attack turned himself in Wednesday night. Mourad Hamyd, 18, surrendered at a police station after learning his name had been linked to the case in the news, said Agnes Thibault-Lecuivre, spokeswoman for the Paris prosecutor.

She did not specify his relationship to the Kouachis.

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Dilanian reported from Washington. Associated Press writers Jamey Keaten and Raphael Satter in Paris contributed.

Associated Press writer Raphael Satter contributed to this story.

Police in France search for shooting suspects

An armed French policeman aims for a shot as he patrols in Fleury, north of Paris, France, Thursday, Jan. 8, 2015. (AP / Thibault Camus)

SWAT police officers near Paris

SWAT police officers patrol in the village of Longpont, northeast of Paris, in search of the two heavily armed brothers suspected in the massacre at Charlie Hebdo newspaper, Thursday, Jan. 8, 2015. (AP / Michel Spingler)

French riot officers patrol in Longpont

French police officers patrol in Longpont, north of Paris, France, Thursday, Jan. 8, 2015. (AP / Thibault Camus)

Gas station in Villers Cotteret

A police van is parked in a gas station in Villers Cotteret, 80 km northeast of Paris, Thursday, Jan. 8, 2015, where the suspects were reportedly spotted, a day after masked gunmen stormed the offices of a satirical newspaper and killed 12 people. (AP / Michel Spingler)

Croix Rouge neighbourhood in Reims

A police officer stands guard in front of a building where forensic police officers look for evidence relating to the three suspects of the shooting attack at the satirical French newspaper Charlie Hebdo's headquarters in Paris, in an apartment located in the Croix Rouge neighbourhood in Reims, east of France, Thursday, Jan. 8, 2015. (AP / Thibault Camus)

Hunt for suspects

A police officer stands guard in front of a building where forensic police officers look for evidence relating to the three suspects of the shooting attack at the satirical French newspaper Charlie Hebdo's headquarters in Paris, in an apartment located in the Croix Rouge neighborhood in Reims, east of France, Thursday, Jan. 8, 2015. (AP / Thibault Camus)

Paris Prefecture control

Police officers work at Paris Prefecture control room in Paris, Thursday Jan. 8, 2015. (AP / Remy de la Mauviniere)

Paris security

A heavily armed police officer guards the General Directorate for Internal Security headquarters, seen behind, in Levallois Perret, outside Paris, Thursday, Jan. 8, 2015. (AP / Christophe Ena)

French Prime Minister Manuel Valls

French Prime Minister Manuel Valls addresses reporters following a crisis meeting with President Francois Hollande at the Elysee Palace in Paris, Thursday Jan. 8, 2015. (AP / Remy de la Mauviniere)