HOUSTON -- Officials of the Federal Bureau of Investigation (FBI) said on Thursday that 14 people were confirmed dead when an attacker rammed a pickup truck into New Year's Day revelers in New Orleans one day earlier.

The attacker was shot dead in gunfight with responding police officers. New Orleans Coroner Dr Dwight McKenna previously announced 15 deaths.

The FBI now believes the attacker is likely to be a lone wolf terrorist with no known accomplices, Christopher Raia, deputy assistant director of the FBI counterterrorism division, said at a press conference on Thursday. FBI officials said Wednesday that they "do not believe that Jabbar was solely responsible".

"We do not assess at this point that anyone else is involved in this attack except for Shamsud-Din Jabbar, the subject you've already been briefed on," said Raia.

Jabbar, 42, a US citizen living in Houston, Texas, had previously served in the US Army and was struggling with financial troubles in recent years, local media reported, citing court documents.

"First and foremost, let me be very clear about this point, this was an act of terrorism,"Raia said. "It was premeditated and an evil act."

So far there is not a "definitive link" between the New Orleans attack and the Las Vegas explosion as it is still "very early" in the investigation, he added.

A Tesla Cybertruck exploded outside a Trump hotel in Las Vegas on Wednesday, killing the driver and injuring seven others nearby. Police said a combination of fireworks, gas tanks and camping fuel in the bed of the vehicle had been detonated by a device controlled by the driver.

"At this point, there is no definitive link between the attack here in New Orleans and the one in Las Vegas," Raia said, adding it is very early in investigation.

Louisiana Governor Jeff Landry said at a news conference that an attack like the one on Bourbon Street can happen anywhere, and "you have to crush" evil to protect Americans.

Bourbon Street, where the truck attack happened in the heart of New Orleans, will reopen Thursday afternoon, according to New Orleans Mayor LaToya Cantrell.