Chattanooga shootings: Four Marines killed at Tennessee US Navy centres
A gunman has killed four US Marines and injured several others at two US Navy buildings in Chattanooga, Tennessee.
A local district lawyer said the shootings were being investigated as an "act of domestic terrorism".
The gunman, who was shot dead, was named as 24-year-old Mohammad Youssuf Abdulazeez by the FBI and local reports said he was born in the Middle East.
President Barack Obama said the attack was "heartbreaking" and said the suspect appeared to be a "lone gunman".
Abdulazeez is believed to have been born in Kuwait, but has lived in the US for several years.
He was arrested earlier this year in Chattanooga for driving under the influence of alcohol.
A spokesman for the University of Tennessee at Chattanooga said a student with the same name graduated in 2012 with a degree in engineering, according to local media reports.
The Chattanooga Times newspaper reported that he went to a local high school and competed on the wrestling team.
He left this message in his school yearbook: "My name causes national security alerts. What does yours do?"
Analysis: By Gary O'Donoghue, BBC News, Tennessee
The investigation is still at an early stage, but it appears that Muhammad Youssef Abdulazeez was acting alone. What made him do what he did will be the subject of intensive inquiries that will delve deep into his past and that of his friends and family, and into his state-of-mind.
But lone wolves, as such men are often described, are the hardest to stop.
Both the president and the head of the FBI have recently underlined this problem and called on local communities to be vigilant for the signs of any radicalisation.
It is also hard for the authorities to protect all potential targets. The first location at which Abdulazeez began firing was an army recruitment office, in the middle of a strip mall - flanked by a mobile phone shop and an Italian restaurant - in other words, firmly within the local community. Many will not want the military to completely retreat behind barbed wire and concrete barriers.
Armed police raided the house where he lived, a few miles outside Chattanooga in Hixson, after the shootings and an AP reporter said two women were led away in handcuffs.
In a statement, the FBI confirmed his identity but said it "would be premature to speculate on the motives of the shooter at this time".
Officials told the AP news agency that Abdulazeez was not known to federal law enforcement before the attacks.
Earlier, US officials said authorities were investigating whether the gunman was inspired by or had links to the Islamic State (IS) group or other jihadist organisations.
IS leaders have called on their followers to launch attacks during the month of Ramadan, which comes to an end this weekend.
FBI agent Ed Reinhold, who is leading the investigation, said the first shooting occurred at about 10:45 local time (14:45 GMT) at a US Navy recruitment centre in the east of the city.
After opening fire on the building, the gunman then fled the scene in a Ford Mustang and was pursued by Chattanooga police, Mr Reinhold told reporters.
He was shot dead after a gunfight at a US Navy reserve centre about seven miles (10 km) away on Amnicola Highway.
The US Marines confirmed in a statement that there were "four Marine fatalities" at the Navy and Marine Corps Reserve Centre in Chattanooga.
They said one Marine Corps recruiter was wounded but was later released from hospital. Two other people are believed to have been treated for injuries.
"This is a sad day for the United States. These service members served their country with pride," Bill Kilden, the federal prosecutor for eastern Tennessee, said.
"We are investigating this as an act of domestic terrorism," he told reporters.
But other officials expressed caution at jumping to conclusions.
"We are looking at every possible avenue - whether it was terrorism, whether it was domestic, international or whether it was a simple criminal act," Mr Reinhold said.
City Mayor Andy Berke tweeted: "Horrific incident in our community."
"Our hearts are broken for the families of the four Marines killed in today's terrible act of violence. They are in our prayers," he added.
'A lot of shots'
Eyewitnesses reported seeing the gunman firing from inside a car outside the recruitment centre.
Gina Mule, who works at a local restaurant, told CNN she heard "really loud noises" and saw a man with a "high-powered rifle".
"A lot of shots were fired," she added.
A statement from the US Department of Homeland Security said it was "enhancing the security posture at certain federal facilities, out of an abundance of caution".
Recent incidents at US military recruitment centres
- December 2010: Muhammad Hussain planned to detonate a bomb at a centre in Catonsville, Maryland, but the plot was foiled by FBI.
- June 2009: Abdulhakim Muhammad carried out a drive-by shooting outside a centre in Little Rock, Arkansas. One person was killed and another was wounded.
- March 2008: Unnamed bombers set off explosives near a Times Square centre in New York City. No one was hurt in the blast.