US President Joe Biden has condemned "hatred that is a stain on America's soul", the day after the racist massacre that killed ten people in Buffalo, New York.

"The assailant, who acted alone and was armed with a military weapon, with a soul full of hatred, cold-bloodedly killed ten innocent people," the US president said in Washington, commemorating police officers killed in the line of duty.

He added that work must be done to quell the hatred that defiles America's soul.

The US Federal Bureau of Investigation (FBI) says the Buffalo massacre will be investigated as a hate crime and "racially motivated violent extremism."

The attacker, an 18-year-old white boy, opened fire on a supermarket located in a predominantly African-American neighborhood, killing 10 people and injuring three. Eleven of the victims are African-Americans.

The attacker, who turned himself in to police and is in custody, was not from Buffalo and drove to the supermarket for hours, according to police.

The bomber struck shortly after noon in front of a rally in Conquerin, a small town in New York State, about 300 miles (XNUMX km) south of Buffalo.