By Harriet McLeod

CHARLESTON, S.C. (Reuters) - A U.S. judge said on Wednesday he will hold a closed-door hearing next week on whether accused white supremacist Dylann Roof is mentally competent to stand trial for the shooting deaths of nine black parishioners in South Carolina last year.

U.S. District Judge Richard Gergel scheduled for Monday a hearing on competency concerns raised by defense attorneys earlier this month for the first time.

The question arose as final jury selection was due to begin in a federal case against 22-year-old Roof, who faces 33 counts of hate crimes, obstruction of religion and firearms charges in the shooting deaths of nine people at Emanuel African Methodist Episcopal Church in Charleston, South Carolina in June 2015.

Final jury selection, which has been on hold, will resume on Nov. 28, if Roof is found competent to stand trial. The judge has ordered an evaluation into whether Roof has the capacity to understand the legal proceedings and help attorneys defend him.

Gergel closed the hearing on the matter over the objections of prosecutors and media outlets.

"The Court finds it wholly impractical to conduct a proper competency hearing in this matter without running the substantial risk of disclosing information that would prejudice Defendant's right to a fair trial and an impartial jury," he said in a ruling on Wednesday.

Federal prosecutors have said Roof planned the attack for months, singling out victims who were black and elderly. They are seeking the death penalty.

Roof, who has said he would plead guilty if that potential punishment was dropped, also faces the death sentence in a state murder trial scheduled for next year.

Gergel did not say when he would rule on Roof's competency.

(Editing by Letitia Stein and Matthew Lewis)