Paris airport employees are among the subjects of French investigations into Islamic radicalization in the country, CNN reported Wednesday. Public transport operators are also being investigated.

The investigations began a "couple of years" before the Nov. 13 Paris assaults for which the Islamic State group has claimed responsibility, a French counterterrorism source told CNN. Among the divisions and locations French intelligence is investigating are the national railway service SNCF, Paris public transport company RATP and airports such as Charles de Gaulle and Orly.

One of the assailants reportedly involved in the massacre at the Bataclan theater was a bus driver for RATP until October 2012. Samy Amimour, 28, had been flagged by French intelligence services in 2012 when he was "placed under supervision after anti-terrorism authorities investigated an aborted attempt to travel to Yemen," according to CNN. He was charged with activities in collaboration with a terrorist enterprise.

In the United States, similar threats regarding transportation were flagged by authorities in a June Department of Homeland Security Inspector General report. The study found that 73 aviation employees who had links to terrorist activities had not been identified by the Transportation Security Administration, NBC News reported. The oversights were the result of the TSA not being "authorized to receive all terrorism-related information under current interagency watchlisting policy," the report said.

"Without complete and accurate information, TSA risks credentialing and providing unescorted access to secure airport areas for workers with potential to harm the nation's air transportation system," the report found.

The report recommended that the TSA request additional watch list data, require that airports improve job application verification to work and rescind credentials when working documents expire.