Story highlights Chattanooga shootings were "motivated by foreign terrorist organization propaganda," FBI chief says

Comments mark first time U.S. official has explained why Chattanooga was thought to be terrorism

Mohammad Abdulazeez shot and killed four U.S. Marines and a sailor in July

New York (CNN) The fatal shootings at a Navy reserve facility in Chattanooga, Tennessee, in July were "motivated by foreign terrorist organization propaganda," FBI Director James Comey told reporters Wednesday in New York.

"There is no doubt that the Chattanooga killer was inspired, motivated by foreign terrorist organization propaganda," Comey said, adding it's difficult to determine which terrorist group may have inspired Abdulazeez.

Photos: Deadly shooting in Chattanooga, Tennessee Photos: Deadly shooting in Chattanooga, Tennessee An FBI investigator works outside a military recruiting center where a gunman opened fire Thursday, July 16, in Chattanooga, Tennessee. Authorities say Mohammad Youssuf Abdulazeez, 24, opened fire first on the recruiting station and then moved to a U.S. Navy facility seven miles away. At the Navy facility, he fatally shot four U.S. Marines and wounded three other people before he died in police gunfire. A U.S. Navy sailor later died from his wounds. Hide Caption 1 of 12 Photos: Deadly shooting in Chattanooga, Tennessee Abdulazeez was born in Kuwait and had Jordanian citizenship, law enforcement officials said. He was a naturalized U.S. citizen. Hide Caption 2 of 12 Photos: Deadly shooting in Chattanooga, Tennessee A woman places a balloon and flowers at a makeshift memorial outside the military recruiting center on Friday, July 17. Hide Caption 3 of 12 Photos: Deadly shooting in Chattanooga, Tennessee The Rev. Drew McCallie prays during a church service in Chattanooga on July 16. Hide Caption 4 of 12 Photos: Deadly shooting in Chattanooga, Tennessee Members of the FBI gather evidence at the scene of the recruiting center shooting on July 16. Hide Caption 5 of 12 Photos: Deadly shooting in Chattanooga, Tennessee A police car blocks the entrances to the U.S. Navy Reserve Center on July 16. Hide Caption 6 of 12 Photos: Deadly shooting in Chattanooga, Tennessee A car believed to be driven by Abdulazeez is seen on the grounds of the Navy facility. Hide Caption 7 of 12 Photos: Deadly shooting in Chattanooga, Tennessee WTVC's Drew Bollea heard gunshots on Amnicola Highway near the Navy facility. Hide Caption 8 of 12 Photos: Deadly shooting in Chattanooga, Tennessee The gunman first opened fire at this military recruitment office located in a strip mall off Lee Highway in Chattanooga. Hide Caption 9 of 12 Photos: Deadly shooting in Chattanooga, Tennessee The entrance to the military recruiting office is seen riddled with bullet holes on July 16. Hide Caption 10 of 12 Photos: Deadly shooting in Chattanooga, Tennessee Blue evidence markers, believed to be the location of spent shell casings, can be seen here. Gina Mule, a server at a restaurant who took this photo, said she saw a man in a car firing a "high-powered rifle" at the recruiting offices at about 10:50 a.m. ET Thursday. Hide Caption 11 of 12 Photos: Deadly shooting in Chattanooga, Tennessee An officer patrols the parking lot of the recruitment center. Hide Caption 12 of 12

The FBI has been investigating the shootings as a terrorism case from the outset, Comey said.

His comments mark the first time a U.S. official has provided details outlining why the Chattanooga shootings are thought to be an act of terrorism. Earlier this month, President Barack Obama cited the Chattanooga shootings along with the recent San Bernardino, California, attacks as terrorist incidents but did not elaborate.

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