FBI director James Comey said Wednesday that the attacks on two military facilities in Chattanooga, Tennessee, earlier this year were motivated by terrorist propaganda.

"There is no doubt that the Chattanooga killer was inspired, motivated by foreign terrorist organization propaganda," Comey informed reporters in New York, according to CNN.

Muhammad Youssef Abdulazeez was responsible for the July 16 shootings, which he carried out first at a military recruiting center and then a Navy reserve facility nearby in Chattanooga. Abdulazeez killed four U.S. Marines and one sailor in the attack.

Comey also said Wednesday that it was difficult to narrow down which terror group inspired the gunman.

Abdulazeez, who was killed in a shootout with police, was born in Kuwait and became a U.S. citizen in 2003. He had traveled multiple times to Jordan, one trip occurring as recently as last year. His father was also investigated by the FBI twice in a probe related to terrorism funding but was cleared of wrongdoing.

The FBI has been investigating the shootings as an act of terrorism.

Concerns about terrorism have risen in the United States following the attacks in Paris and San Bernardino, California, that together killed almost 144 people. Currently, Americans name terrorism as the top issue facing the country, according to a Gallup poll released this week.