The alleged defector was associated with Al-Qaeda militants in Syria suspected of plotting to smuggle non-metallic bombs aboard passenger aircraft bound for Western countries, ABC television reported, citing two unnamed intelligence officials.
The targeting of the defector was first reported by the McClatchy news service.
According to the reports, European intelligence sources describe the former agent -- who allegedly defected from either French military intelligence services or the country's foreign spy agency the DGSE -- as the "highest ranking defector ever to go over to the terrorist group."
The French national, who reportedly joined Al-Qaeda in Afghanistan and went to Syria, was one of the targets of a round of US air raids in Syria aimed at the Al-Nusra Front, Al-Qaeda's Syrian affiliate, McClatchy wrote. US officials at the time said the air strikes were aimed at the "Khorasan" group, describing it as a collection of Al-Qaeda veterans.
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The United States has launched a bombing campaign in Syria and Iraq as part of a coalition fighting jihadists in both countries -- mainly those belonging to the radical Islamic State group that controls large swathes of territory.
France's defence ministry denied any of its former agents was involved. "The report that the person allegedly belonged to the defence ministry's intelligence services is completely and utterly wrong," a ministry official told AFP.
The DGSE, meanwhile, refused to comment, as did France's foreign ministry.
According to the McClatchy report, the alleged former officer is an expert in explosives and is still alive despite the air strikes.
In Washington, the Central Intelligence Agency and the US military declined to comment.