OXFORD, Miss (Reuters) - A former Ku Klux Klansman who was serving three life sentences for his role in the 1964 killings of two black teenagers in Mississippi has died, a federal prisons bureau spokesman said on Wednesday.

James Ford Seale, 76, died on Tuesday after being found unresponsive at the correctional facility in Terre Haute, Indiana, where he was housed, Bureau of Prisons spokesman Edmond Ross told Reuters.

He was pronounced dead just before 6 a.m. local time at the hospital where he had been transported, Ross said.

Seale was convicted in 2007 of kidnapping and conspiracy charges connected to the deaths of Henry Hezekiah Dee and Charles Eddie Moore, who were kidnapped while hitchhiking in Mississippi.

Dee and Moore, both 19, were taken to a national forest, where Seale trained a shotgun on the teenagers while his companions beat them.

The two young men were then stuffed into the trunk of a car, driven to a tributary of the Mississippi River, attached to heavy weights and thrown alive into the water from a boat, prosecutors said.

Their bodies were only recovered during a high-profile search later that year for three civil rights activists whose deaths generated widespread revulsion at the racial violence in Mississippi.

Seale's trial was part of an effort by federal prosecutors to clear up crimes committed during the 1950s and 1960s by white supremacists who aimed to terrify the black community into not supporting a campaign for civil and voting rights for African-Americans in the racially segregated South.

Prosecutors reopened the case in 2005 at the urging of Moore's brother. Eight men were implicated in the killings but only two were still alive when charges were filed -- Seale and a man who was granted immunity in exchange for testifying against him.

(Reporting and Writing by Colleen Jenkins; Additional reporting by Jacob Batte in Oxford; Editing by Greg McCune)