FBI's paranoia evident in full text of infamous letter to Martin Luther King

A vicious letter written by the FBI and sent to US civil rights champion Martin Luther King has been made public in full.

The one-page, anonymous letter was sent to King in 1964, calling him a "complete fraud and a great liability", an "evil, abnormal beast", and threatening to expose his marital infidelities in an apparent bid to make him commit suicide.

Heavily censored copies of the letter have circulated for years but The New York Times on Wednesday published the note almost in its entirety, blanking out a woman's name.

The letter highlights the hostile attitude the FBI, which at the time was run by J. Edgar Hoover, had towards King and the civil rights movement.

According to the Times, it was written by one of Hoover's deputies, William Sullivan, and apparently was sent along with an audio recording containing evidence of King's affairs.

"Listen to yourself you filthy, abnormal animal," the letter reads. "You have been on the record, all your adulterous acts, your sexual orgies extending far into the past. This one is but a tiny sample."

When King received the letter, he told friends that someone wanted him to kill himself, the Times reported.