CHICAGO (AFP) - The man who killed five US troops in Tennessee was suicidal, preparing for bankruptcy and struggling with drug abuse, a family representative told local media.

Four US marines and a sailor were killed after 24-year-old Mohammad Youssuf Abdulazeez opened fire on two military centers in Chattanooga on Thursday, before dying himself in a shootout with police.

Authorities have said they are treating the case - a grisly scene reminiscent of other shooting rampages at US military installations - as an "act of terrorism." However, a family representative painted Abdulazeez as an emotionally troubled young man who had shown no outward signs of radicalization.

A diary obtained by the FBI showed he wrote about having suicidal thoughts and "becoming a martyr" in 2013 after having lost his job to drug use, the family representative told ABC News.

In the months before the shooting, he was having problems coping with a 12-hour overnight shift at a new job and started taking sleeping pills, the representative said. He was also abusing painkillers and marijuana and was thousands of dollars in debt.

His parents had sent Abdulazeez to stay with family in Jordan in hopes of getting him away from friends who were a bad influence, the representative said. They had also tried to get him treatment for his mental illness.

Investigators are examining his overseas travel to see if Abdulazeez came into contact with extremists.

The family representative told ABC that Abdulazeez "was susceptible to bad influences" and would be affected by watching news accounts of "children being killed in Syria." However, a friend told CNN that Abdulazeez thought extremists like the Islamic State group were "doing wrong" and "it was a stupid group and it was completely against Islam."