A man has driven a truck through a crowd of people in the US city of New Orleans, killing at least 15 and wounding at least 30 more.
The FBI says the driver was a 42-year-old army veteran from Texas, and an Islamic State flag was attached to the tow bar of his truck.
Suspected bombs were later found in the area.
Here's what we know so far.
What happened?
The driver crashed a pick-up truck through a crowd of people about 3:15am on Wednesday, local time.
The victims were celebrating New Year's Day in the Bourbon Street party area, in the city's French Quarter.
Police said the driver drove around a barrier and onto a footpath and tried to "run over as many people as he possibly could". He was driving at a "very fast pace".
"He was hell-bent on creating the carnage and the damage that he did," New Orleans Police Superintendent Anne Kirkpatrick said.
He then got out of the truck and started firing a gun.
Police returned fire, killing the driver.
Two officers were shot but stable, police said.
Investigators later found multiple suspected improvised explosive devices (IED) in the truck.
"Other potential IEDs were also located in the French Quarter," FBI special agent Alethea Duncan said. "As of now, two IEDs have been found and rendered safe."
Who was the driver?
The FBI named the driver as Shamsud-Din Jabbar.
He was a US citizen from Texas. He served in the US Army for 13 years and was deployed to Afghanistan for a year in 2009, an army official told Reuters.
He served first as an HR specialist and an IT specialist from 2007 until 2015. He then joined the Army Reserve as an IT specialist until 2020, holding the rank of staff sergeant at the end of service, according to the official.
Corporate records show that Jabbar got involved in a series of businesses in recent years.
In a YouTube video from 2020, a man with his name said his time in the military had taught him the importance of great service and taking everything seriously.
"I've taken those skills and applied them to my career as a real estate agent, where I feel like what really sets me apart from other agents is my ability to be able to be a fierce negotiator," he said in the video.
In the hours before the attack, Jabbar posted videos to social media indicating that he was inspired by the ISIS terrorist group, US President Joe Biden said, citing the FBI.
The Ford pick-up truck he used in the attack had been rented through a car-sharing app known as Turo.
"An ISIS flag was located in the vehicle, and the FBI is working to determine the subject's potential associations and affiliations with terrorist organisations," it said in a statement.
The FBI confirmed its investigators were conducting an operation at a property in Houston, Texas, in an area matching one of Jabbar's known residences.
Turo said in a statement that there was no criminal background information about Jabbar that would have identified him prior to the incident in New Orleans.
The company said its safety team is working with law enforcement agencies to share information that could help their investigations.
Who was affected?
Officials have not yet released the names of the 15 people killed in the New Orleans New Year's Day truck attack, but their families and friends have started sharing their stories.
Zion Parsons from Gulfport, Mississippi, had been celebrating New Year's Eve at his first night on Bourbon Street when he said the vehicle appeared and ploughed into his friend, Nikyra Dedeaux, 18, who had dreamed of becoming a nurse.
"A truck hit the corner and comes barrelling through throwing people like in a movie scene, throwing people into the air," Mr Parsons told The Associated Press.
"It hit her and flung her, like, at least 30 feet and I was just lucky to be alive."
Reggie Hunter, a 37-year-old father of two from Baton Rouge, was also among the people killed, according to his cousin, Shirell Jackson.
Kim Broussard, the athletic director at St. Thomas More Catholic High School in Lafayette, revealed on Wednesday that Tiger Bech, 27, a former high school and college football player from Louisiana, was also among those who died in hospital.
Kimberley Usher, the owner of Kimmy's Deli in Metarie, Louisiana, told AP that Nicole Perez — a manager at Ms Usher's store and a single mother of a four-year-old — had died in the attack.
They were in an area that ordinarily would have been blocked by bollards designed to prevent such attacks.
But the bollards had been malfunctioning and had been removed for repairs.
Police said a patrol car and other barriers were in place instead, but the driver was able to get around them.
"So we did indeed have a plan, but the terrorist defeated it," Superintendent Kirkpatrick said.
Is there an ongoing threat?
Authorities suspect the driver was not acting alone.
"We do not believe that Jabbar was solely responsible," Ms Duncan said. "We are aggressively running down every lead, including those of his known associates."
When questioned at a press conference, authorities would not provide further information.
"Why would we tell you that?" Louisiana Governor Jeff Landry said when asked why they were confident multiple suspects were involved.
"We want to answer pertinent questions, but anything that would lead to impeding or endangering this investigation is not going to be said."
An internal police document, seen by the Associated Press, said surveillance cameras captured vision of what appeared to be three men and a woman placing an IED in the area.
However, investigators no longer believe they were involved, CNN reported, citing a law enforcement official.
Superintendent Kirkpatrick said police had conducted a sweep of every street in the French Quarter, "looking for suspicious packages, bags, ice chests, you name it".
The city had been preparing to host the Sugar Bowl, an annual college football event that attracts thousands of people, later on Wednesday. It has been postponed for 24 hours.
"Part of the safety plan is, we have bomb dogs out there sweeping the Superdome [stadium] and all the exterior area, and we're locking that down," Superintendent Kirkpatrick said.
What's happening now?
The injured victims have been taken to at least five hospitals across New Orleans.
Superintendent Kirkpatrick said the police department had called in "every officer that we have".
The FBI is leading the investigation. It has asked members of the public to contact the agency if they had contact with Jabbar in the 72 hours before the attack.
Mr Biden said he had instructed his team to make every resource available to figure out what happened and ensure there was no remaining threat.
He said investigators were also looking into any links between the attack and an explosion in Las Vegas. One person was killed when a Tesla Cybertruck blew up outside the Trump International Hotel later on Wednesday, local time.
"Our hearts are with the people of New Orleans after this despicable attack," Mr Biden said.
President-elect Donald Trump said his incoming administration would "fully support the City of New Orleans as they investigate and recover from this act of pure evil".
ABC/wires
