The death toll from a New Year's Day vehicle attack in the southern US city of New Orleans has risen to at least 15. The suspect was killed in a shootout with police.

The Federal Bureau of Investigation is investigating the incident as an act of terrorism. The FBI identified the suspect who was driving the vehicle as 42-year-old Shamsud-Din Jabbar, from Texas.

An FBI official told reporters that the agency does not believe the driver was solely responsible and said, "We are aggressively running down every leads, including those of his known associates."

The man rammed a pickup truck into a crowd in the popular French Quarter in the early hours of Wednesday. The area was packed with people celebrating the New Year.

Major US media say dozens of people were injured.

The FBI said a flag of the Islamic State group, and what looked like an explosive device, were found in the vehicle. It also said other potential explosive devices were located in the French Quarter.

The FBI said it is working to determine if the suspect had an association with the group and whether he had any associates.