An alleged Al-Qaeda agent and US citizen involved in a bloody shooting in Yemen five days ago was revealed Friday to have worked for a US nuclear power plant company between 2002 and 2008.

Sharif Mobley, said by a source close to the police in Yemen to hold both US and Yemeni citizenship, was employed by PSEG Nuclear in New Jersey as a laborer, company spokesman Joseph Delmar said.

Mobley, whose name in Yemen is spelled Mobayli, worked "mainly during refueling outages for several weeks at a time" when he was employed by PSEG, the company said in a statement.

"While working here, he did routine labor work carrying supplies and assisting maintenance activities. He also worked at other nuclear plants in the region."

The revelation highlighted US security officials' greatest challenges -- keeping tabs on militants holding American passports and the ultimate fear of an attack involving a dirty bomb or inside a nuclear power station.

Delmar said the man, who grew up in New Jersey, had not been considered a risk.

"This individual satisfied federal security background checks required to work in the US nuclear industry as recently as 2008."

Delmar said no further details could be publicized because of an ongoing investigation. "We are cooperating with law enforcement," he said.

Mobley is accused in Yemen of being a member of Al-Qaeda and shooting a guard while attempting to escape custody on Sunday in the capital Sanaa.

He grabbed a firearm while being treated under guard at a hospital, killed one guard and badly wounded another before being subdued.

Yemeni authorities intensified their campaign against the country's Al-Qaeda branch after it claimed a botched Christmas Day bid to blow up a US passenger plane over Detroit.

US news reports quoted high school classmates of Mobley in New Jersey saying that he had been a friendly boy, known for his karate skills and outgoing personality.

He had not been in any trouble with the law, Fox news and other outlets reported.

After school, Mobley, who is of Somali heritage, became active in organizing pilgrimages for Muslims and himself went to Yemen ostensibly to study Arabic, the Daily News reported.

US Central Command chief General David Petraeus said last month that Yemen is the one part of the Middle East where Al-Qaeda remains a growing threat.

"Our assessment is that over the course of the last year or so, Al-Qaeda has been diminished in that area," Petraeus, said referring to his zone of command stretching from east Africa through the Middle East to Pakistan and Kazakhstan.

The United States has reportedly supplied Yemen with intelligence and other support in its operations against Al-Qaeda.

In January, a group of Yemeni clerics called for a jihad, or a holy war, if the United States undertook direct military intervention.