A previously unknown audio tape of an interview with slain civil rights leader Martin Luther King Jr was discovered recently in the attic of a Tennessee home, and a New York collector who bought the recording said he plans to offer it for sale next week.

The 10-minute reel-to-reel recording was made on Dec 21, 1960, nearly three years before King's famed "I Have a Dream" speech and more than seven years before he was gunned down in Memphis, Tennessee, collector Keya Morgan said on Thursday.

Morgan, the proprietor of a Manhattan gallery that deals in historical manuscripts, photos and other artifacts, described the tape as an extremely rare discovery.