The man charged with killing nine black parishioners last year in a US church should face the death penalty, Attorney General Loretta Lynch said.
Dylann Roof is awaiting trial in connection with the massacre at Emanuel AME Church in Charleston, South Carolina, on June 17.
Ms Lynch said the US justice department will seek the death penalty: "The nature of the alleged crime and the resulting harm compelled this decision."
The department had considered "all relevant factual and legal issues", she said.
Roof faces federal hate crime charges in connection with the killings, which contributed to a national conversation about race relations and ultimately led to the removal of a Confederate battle flag from the grounds of the South Carolina Statehouse.
He is also charged in state court with nine counts of murder, and South Carolina prosecutors have already announced plans to seek the death penalty when he stands trial on those charges next year. Solicitor Scarlett Wilson has said she wants her case to be tried first.
Roof, who is white, appeared in photos waving Confederate flags and burning or desecrating US flags, and purportedly wrote of inflaming racial violence. Survivors told police that he hurled racial insults during the attack.
He was arrested a day after the shootings when a motorist spotted his Confederate number plate.
Federal prosecutors charged Roof with hate crimes a month after the shooting, saying he was motivated by racial hatred and a desire to commit a "notorious attack" when he opened fire inside the church.
Ms Lynch said at the time: "To carry out these twin goals of fanning racial flames and exacting revenge, Roof further decided to seek out and murder African-Americans because of their race."
Though the justice department says it is committed to seeking the death penalty, federal executions are exceedingly rare.
The last time a federal defendant was put to death was in 2003, and President Barack Obama has said he is "deeply concerned" about the death penalty's implementation.
Roof's lawyers in the federal case have said their client would be willing to plead guilty if the death penalty were not on the table.
The only other person charged in connection with the case has already pleaded guilty. Joey Meek, a friend with whom Roof spent time in the days before the shootings, last month admitted lying to federal authorities. He has agreed to help with the prosecution against Roof.
At Roof's initial appearance before a judge, several relatives of the shooting victims said they forgave the alleged shooter and that they would pray for him.
On Tuesday, Malcolm Graham, brother of shooting victim Cynthia Hurd, said prosecutors had talked to family members before announcing the decision and he felt it was "an appropriate punishment".
Mr Graham said: "What he did that night was kill innocent individuals at a Bible study. Not only was it an attack on those who were there, it was an attack on a race of people."