The white gunman who killed 10 black people in a racist attack at a US supermarket has been charged with federal hate crimes that could potentially carry a death penalty.

The criminal complaint filed against Payton Gendron coincided with a visit to Buffalo, New York, by Attorney-General Merrick Garland.

He met with the families of the people who were killed and placed a bouquet of white flowers at a memorial outside the Tops Friendly Market, which has been closed since the May 14 attack.

“No one in this country should have to live in fear that they will go to work or shop at a grocery store and will be attacked by someone who hates them because of the color of their skin,” Mr Garland said at a news conference on Wednesday.

Mr Garland, who halted federal executions last year, did not rule out seeking the death penalty against Gendron, 18.

He said “families and the survivors will be consulted” as the Justice Department weighed whether to seek capital punishment.

The federal hate crimes case is based partly on documents in which Gendron laid out his radical, racist worldview and extensive preparation for the attack, some of which he posted online and shared with a small group of people shortly before he started shooting.

So far, the evidence made public against Gendron suggests he acted alone, but Mr Garland and Deputy FBI Director Paul Abbate said investigators were examining the gunman’s communications with others before the shooting.

– AAP