A teenager accused of killing 10 people and injuring three others in a mass shooting at a US supermarket in the city of Buffalo is on suicide watch, officials say.

Payton Gendron is being detained separately from other individuals in a holding centre following the massacre on Saturday afternoon.

Eleven of the 13 people who were shot were black.

The 18-year-old suspect, who is white, was arraigned on first-degree murder charges hours after the shooting, to which he pleaded not guilty.

Authorities are calling the shooting an act of “violent extremism” motivated by racial hatred.

Police said the the suspect, of Conklin, New York, drove about 200 miles (320 km) from his home to the store and, wearing military gear, used a helmet camera to livestream the attack.

For at least two minutes, he broadcast the shooting on the streaming platform Twitch before the service ended his transmission.

Buffalo attack: Gunman live-streamed ‘racially-motivated’ mass shooting that killed at least 10 at supermarket in New York state

Letitia James, the attorney general of New York, said the attack was committed by a “sick, demented individual who was fuelled (by) a daily diet of hate”.

Ms James said her office will be investigating social media following the atrocity.

She added: “Let us come together as one and let us put aside any differences and let us all stand and remember the words of Dr (Martin Luther) King, that love, only love, will overcome hate.”

The attack happened at the Tops Friendly Markets in Jefferson Avenue, about three miles (5km) north of downtown Buffalo in New York state.

According to police, the gunman began shooting in the car park before moving inside the supermarket. Four were shot outside, including three fatally.

Security guard Aaron Salter fired multiple shots but none penetrated the gunman’s armour. The perpetrator killed Salter and made his way through the aisles, shooting shoppers.

The gunman was confronted by police and put his rifle to his own neck, but then surrendered and dropped the weapon.

Federal agents have interviewed the suspect’s parents and have served multiple search warrants.

Federal authorities were still working to confirm the authenticity of a 180-page manifesto that was posted online, which detailed the plot and identified Gendron by name as the gunman, an official said.

Meanwhile, Gendron appeared on the police radar last year after he threatened to carry out a shooting at a high school, according to a police official.

New York State Police said troopers were called to Susquehanna High School in Conklin in New York State on 8 June 2021, for a report that a 17-year-old student had made threatening statements.

Police said the student was taken into custody under a state mental health law and taken to a hospital for an evaluation. The police statement did not give the student’s name.

Speaking on Sunday, President Joe Biden said: “We must all work together to address the hate that remains a stain on the soul of America.

“Our hearts are heavy once again, but our resolve must never, ever waiver.”

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