US authorities were investigating on Thursday after an army veteran with an Islamic State flag who was "hellbent" on carnage steered a pickup truck into a crowd of New Year's revelers in New Orleans, killing at least 15 people and wounding dozens.
The FBI identified the attacker as Shamsud-Din Jabbar, a 42-year-old US citizen from Texas. He appeared to have been a real estate agent working in Houston and had served as an IT specialist in the military.
Officials said they were searching for accomplices but gave few details.
Police Superintendent Anne Kirkpatrick described Jabbar as a "terrorist," and the FBI said "an IS flag was located in the vehicle," using another name for the Islamic State jihadist group.
"It was just scary, I cried my eyes out honestly," tourist Ethan Ayersman, 20, told AFP in New Orleans.
He was among the masses visiting the colorful southern US city for New Year's celebrations and said he had enjoyed popular Bourbon Street -- where the deadly assault later unfolded -- into the early hours.
Later on, Ayersman said his brother woke him up after hearing gunshots and a car speeding.
From the window of their nearby rental, they could see "some of the bodies that were being lined up," Ayersman said.
US President Joe Biden, describing the attack as "despicable," said Jabbar had posted videos online hours before "indicating that he was inspired by IS."
Biden also said that law enforcement agencies were probing any possible links between the attack and an explosion later on Wednesday of a Tesla Cybertruck outside a hotel owned by US President-elect Donald Trump in Las Vegas that killed one person, though he cautioned that none had been found so far.
Officials said Wednesday a manhunt was underway, with FBI agent Alethea Duncan warning that authorities "do not believe that Jabbar was solely responsible."
Louisiana Governor Jeff Landry said: "We're hunting some bad people down."
The FBI said it was conducting search warrants in New Orleans "and other states." Earlier, the bureau's field office in Houston, Texas said it was conducting activity "related" to the New Orleans attack.
An FBI spokesman told AFP that 15 people had been killed in the attack, citing the New Orleans coroner's office.
Among the dead, Nikyra Cheyenne Dedeaux, 18, graduated from high school last year and was to begin a nursing program this month, US media reported.
Her mother Melissa Dedeaux told the news website Nola.com that her daughter had snuck out to New Orleans from Gulfport, Mississippi with her cousin and a friend to celebrate the new year.
Reggie Hunter, a 37-year-old warehouse manager and father of two from Baton Rouge, was also killed in the attack, the New York Times reported, citing a relative.
The newspaper also identified Tiger Bech, a former football player at Princeton University, among those killed.
