WASHINGTON/tennessee  - The FBI said on Thursday it had found nothing that ties a man suspected of gunning down four Marines in Chattanooga, Tennessee, to an international terrorist organization.

At a news conference, the FBI said it was still looking for a motive behind the attack on two military facilities that also left three people wounded. The gunman, identified by federal authorities as Mohammod Youssuf Abdulazeez, was also killed. An autopsy would determine the cause of the suspect’s death, Edward Reinhold, special agent in charge of the FBI’s Knoxville, Tennessee, division told reporters. The Department of Defense will decide whether to release the names of the Marines killed, he added.

The gunman who shot and killed four Marines Thursday during two attacks at military facilities in Chattanooga in the US state of Tennessee has been identified as Muhammad Youssef Abdulazeez, according to law enforcement officials.

The Federal Bureau of Investigation said Abdulazeez, 24, who was born in Kuwait, also died Thursday. He became a naturalized United States citizen and went to high school and college in Chattanooga. Although counterterrorism officials had not been investigating Abdulazeez before Thursday’s shooting, federal officials familiar with the inquiry said that his father had been investigated years ago for giving money to an organization with possible ties to terrorists.

At a late night news conference, F.B.I. officials said that thus far they did not have “anything that directly ties” the suspect to international terrorist organizations. The US National Counterterrorism Center also said it has seen nothing so far to connect Abdulazeez to any terrorist organization. But it noted that the Islamic State group (ISIS) has been encouraging extremists to carry out attacks in the US. “We are treating this as an act of domestic terrorism,” said Bill Killian, U.S. Attorney for the Eastern District of Tennessee. At a news conference late Thursday, FBI agent Ed Reinhold said there was "no indication at this point that anybody else was involved."

"Obviously, we're still at the beginning of this investigation," Reinhold said. "We will explore any possibility and that includes whether or not anyone else was involved." US Attorney Killian added that investigators do not believe that there are any more threats to the general public.

President Barak Obama, speaking from the Oval Office shortly after returning from a trip to Oklahoma, vowed a thorough and prompt investigation.

"It is a heartbreaking circumstance for these individuals who have served our country with great valour to be killed in this fashion," Obama said. The Council on American-Islamic Relations (CAIR), a prominent civil rights and advocacy organization, condemned the attack. 

In a statement, CAIR National Executive Director Nihad Awad said: "We condemn this horrific attack in the strongest terms possible. Such inexcusable acts of violence must be repudiated by Americans of all faiths and backgrounds.

"The American Muslim community stands shoulder to shoulder with our fellow citizens in offering condolences to the loved ones of those killed and injured and in rejecting anyone who would harm our nation's safety and security. Our thoughts and prayers are with the families impacted by this tragedy."

The gunman first shot up a recruiting center before driving seven miles to the Navy Operational Support Center and Marine Corps Reserve Center and killing four Marines before he was shot, authorities said. Police chased the gunman from the recruiting center to the Center. The entire attack last about half-an-hour. One of the Marines who was killed was said to b a "decorated war hero with two Purple Hearts." The youngest was 19 years old. Defence officials also said late Thursday a female sailor was in surgery after being shot. Within hours of the bloodshed, law officers with guns drawn swarmed what was believed to be Abdulazeez's house, and two females were led away in handcuffs.

A dozen law enforcement vehicles, including a bomb-squad truck and an open-sided Army green truck carrying armed men, rolled into the Hixson neighborhood, and police closed off streets and turned away people trying to reach their homes. Details of Abdulazeez's life were just beginning to emerge late Thursday. The Chattanooga Times Free Press reported that he graduated from the University of Tennessee at Chattanooga with a Bachelor of Science degree in electrical engineering in 2012. Before that, he graduated from Red Bank High School with a yearbook photo featuring the quote, “My name causes national security alerts. What does yours do?”

Photos of the yearbook photo were sent to the newspaper, which also reported that he was arrested for driving under the influence last April 20. The New York Times,citing law enforcement officials, reported Abdulazeez’s father had been investigated several years ago for possible ties to a foreign terrorist organization and at one point was on - but later removed from – a terror watch list. In a statement, Travis Brickey of the Tennessee Valley Authority, said  the younger Abdulazeez was a student intern "approximately five years ago." The paper also reported that Abdulazeez's father, Youssuf Abdullazeez, was appointed as a "special policeman" for Chattanooga's Department of Public Works in March 2005. Residents and students who knew the suspect said he was a quiet kid, but well-liked. "He was friendly, funny, kind," Kagan Wagner told the Times. "I never would have thought it would be him."