Police lead suspected shooter Dylann Roof into the courthouse in Shelby, North Carolina, in this June 18, 2015, file photo.  [Photo/Agencies]

WASHINGTON - The US Justice Department had decided to seek the death penalty for Dylann Roof, a white gunman charged with killing nine black churchgoers in South Carolina last year, Attorney General Loretta Lynch said on Tuesday.

"Following the department's rigorous review process to thoroughly consider all relevant factual and legal issues, I have determined that the Justice Department will seek the death penalty," said Lynch in a brief statement.

"The nature of the alleged crime and the resulting harm compelled this decision," the statement said.

Roof, then 21, started a shooting spree at the Emanuel African Methodist Episcopal Church in Charleston, a historic black church in the coastal city of Charleston, on June 17, 2015. After his arrest, Roof reportedly told police that he wanted to start a "race war".

Roof had been charged by state attorneys on nine counts of murder and three counts of attempted murder.

He was also indicted on 33 counts of federal charges, including hate crimes.

The racially motivated murder at that time fueled debates of racism in the United States as the country was still recovering from widespread protests and riots in the wake of a series of high-profile police shooting of unarmed African-American men.