Backstreet Boys will kick off Sunday's United We Stand — What More Can I Give benefit in patriotic style by singing "The Star-Spangled Banner," and while Janet Jackson won't appear at the Washington, D.C., show, she will contribute a "video montage" that will be shown during the concert, according to a spokesperson for the event.

Organizers don't yet know what Jackson's video will consist of, and representatives for the singer were unavailable at press time. Veteran singer/songwriter Carole King and '80s pop-rockers Huey Lewis and the News have also been added to the lineup, which includes 'NSYNC, Aerosmith, Michael Jackson and Mariah Carey.

More artists are expected to be announced before the event, the spokesperson said.

Proceeds from the sold-out concert at RFK Stadium will benefit the American Red Cross Liberty Relief Fund, the Salvation Army Relief Fund and the Pentagon Relief Fund.

—Eric Schumacher-Rasmussen