The death toll from an attack on two military centres in Tennessee has jumped to five, following the death of a US sailor.
The US Navy said on Saturday a petty officer succumbed to wounds he sustained in Thursday's shootings in Chattanooga.
The Navy did not identify the sailor, but relatives named him as Petty Officer Randall Smith, a father of three daughters who had recently re-enlisted and transferred to Chattanooga.
"It's hard to understand how somebody can hurt somebody that's serving for you, for your freedom, for your safety," his step-grandmother Darlene Proxmire told WANE television in Indiana.
Four Marines also died in the attack before the gunman, 24-year-old Mohammad Youssuf Abdulazeez, a naturalised US citizen born in Kuwait, was killed in a shootout with police.
Authorities are treating the incident as "an act of terrorism".
The FBI has asked foreign intelligence agencies to help trace Abdulazeez's movements and activities abroad, and analysts will be tracing his activity on social media, officials said.
But it warned against jumping to conclusions, after Michael McCaul, chairman of the House of Representatives homeland security committee, branded the attack "an ISIS-inspired attack."
"At this time, we have no indication that he was inspired by or directed by anyone other than himself," FBI special agent Ed Reinhold said, referring to Abdulazeez.
"We obviously want to know what his thoughts were and who else he was associating with."
The shooting has jarred Chattanooga, a city of 168,000, where the Islamic Society of Greater Chattanooga condemned the attack and cancelled its end-of-Ramadan Eid al-Fitr celebration out of respect for the victims.