The family of the late U.S. civil rights leader Martin Luther King Jr. has decided to auction his personal papers.

Sotheby's, the international auction house, announced the sale, scheduled for June 30. It says the papers will likely bring between $15 and $30 million.

King's archives include 7,000 handwritten items, including sermons, a draft of his Nobel Prize acceptance speech and his "I have A Dream" speech, delivered in Washington in 1963. There are hundreds of hand-written note cards from King's years as a theology student.

The family had tried to sell the archive to libraries and academic institutions but was never offered what it considered a reasonable price.

Sotheby's says it will sell the papers as a single lot to help insure the archive is not split up.

The vice chairman of Sotheby's, David Redden, called King's papers the most important American archive of the 20th century still in private hands. He called King a heroic figure to people around the world.

The sale will come just months after the death of King's widow, Coretta Scott King, who had tried to find an institutional home for the papers.

A deal to sell the archive to the U.S. Library of Congress fell through when members of Congress raised questions about the price.

King led the U.S. civil rights movement in the 1960s, including the campaign to end racial segregation in the South, until his assassination in 1968.

Some information for this report provided by AP.