SANAA, Yemen -- Yemeni authorities suspect that Said Kouachi, one of the brothers involved in the deadly attack on a Paris newspaper, fought with al Qaeda in Yemen at the height of the group's offensive in the country's south, a security official said Friday. U.S. intelligence officials said they believe he was trained by al Qaeda there to return home to carry out an attack.

Witnesses to the assault at the Charlie Hebdo offices in Paris said Said Kouachi claimed allegiance to the Yemeni group during the attack. His 32-year-old brother, Cherif Kouachi, was convicted of terrorism charges in 2008 for ties to a network sending jihadis to fight U.S. forces in Iraq. The brothers were killed Friday in a gunbattle with French police.

A U.S. intelligence assessment described to The Associated Press shows that Said Kouachi was in Yemen for several months in 2011 for training by al Qaeda. The Yemeni security officails said he is believed to have fought with al Qaeda in the Arabian Peninsula, as the branch there is called, in 2011 in Abyan province.

At the time, al Qaeda fighters had taken advantage of a security vacuum during an uprising that eventually ousted President Ali Abdullah Saleh. The militants seized several towns and cities in the south of the country. Abyan province was an al Qaeda stronghold from which the group launched attacks against government forces and new offensives to seize more territory.

The second Yemeni official said Kouachi was believed to be among hundreds of foreigners deported in 2012, when the government expelled many foreign students, fearing they were there under the pretext of studying Arabic but were in fact linking up with al Qaeda.

Both officials spoke to The Associated Press on condition of anonymity because of an ongoing investigation into Kouachi's stay in Yemen.

French authorities knew Kouachi travelled to Yemen, but it's not clear whether they knew what he did there, U.S. officials believe. Still, French authorities placed both Kouachi brothers close surveillance when he returned. The officials believe the brothers led a normal life for long enough that the French began to view them as less of a threat and reduced the surveillance.

A U.S. law enforcement official said both Kouachi brothers had raised enough concern to be placed on the no-fly list. He spoke on condition of anonymity to discuss an ongoing investigation.

One of the foreigners who had been to Yemen earlier was Nigerian Umar Farouk Abdulmutallab, who tried to detonate on a passenger jet over Detroit in December 2009. The Nigerian may have met with radical American-Yemeni cleric Anwar al-Awlaki, linked to al Qaeda, who was suspected of overseeing the operation. Al-Awlaki was killed in a U.S. drone strike in September 2011.

U.S. officials considered al-Awlaki to be an inspirational leader of al Qaeda, and they tied him to the planning and execution of several attacks targeting American and Western interests. Al-Awlaki was also linked to the 2009 shooting rampage at Fort Hood, and was thought to have received emails from the shooter, Maj. Nidal Hasan.

A Yemeni military offensive backed by the United States and neighbouring Saudi Arabia eventually routed militants from many strongholds in southern Yemen. But the group has continued to launch attacks against military and security forces, prompting the U.S. to step up its drone attacks.

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El Deeb reported from Cairo. AP Intelligence Writer Ken Dilanian and AP writer Eric Tucker contributed to this report from Washington.