US President Joe Biden said explosives were found in the vehicle of New Orleans attacker Shamsud-Din Jabbar.

He said the 42-year-old veteran, was inspired by ISIS.

"The FBI has reported to me the killer was an American citizen, born in Texas.  He served in the United States Army on active duty for many years.  He also served in the Army Reserve until a few years ago," Biden said.

Speaking on the explosives found in his vehicle, Biden said: "The FBI also reported to me that mere hours before the attack, he posted videos on social media indicating that he was inspired by ISIS, expressing a desire to kill — a desire to kill."

"The ISIS flag was found in his vehicle, which he rented to conduct this attack.  Possible explosives were found in the vehicle as well, and more explosives were near — were found nearby," he said.

He said the investigation into the incident is currently in its 'preliminary' stage.

The FBI Thursday said the US army veteran motivated by loyalty to the jihadist group Islamic State likely acted alone when he killed and injured dozens in a truck attack against a crowd of New Year revellers in New Orleans, media reports said.

Even as initial concerns predicted that Shamsud-Din Jabbar had accomplices, believed to be on the run, preliminary investigations show he was alone, FBI deputy assistant director Christopher Raia said.

"We do not assess at this point that anyone else was involved," Raia was quoted as saying by Agence France-Presse.

The attack left 15 killed and injured more than 30 in the French Quarter district, which ended only after he was shot by police.