Two men found guilty of the 1965 assassination of civil rights leader Malcolm X are to have their convictions thrown out, one of them posthumously, in an admission by US authorities of a historic miscarriage of justice.

Manhattan District Attorney Cyrus Vance will hold a press conference on Thursday to announce the exoneration of Muhammad A. Aziz and Khalil Islam, his office said Wednesday.

Aziz, 83, was sentenced to life in prison in 1966 but was released in 1985. Also sentenced to life, Islam was released in 1987 and died in 2009.

"These men did not get the justice that they deserved," Vance said in an interview with The New York Times. "What we can do is acknowledge the error, the severity of the error."

The newspaper said that a 22-month investigation conducted jointly by the Manhattan district attorney's office and lawyers for the two men found that prosecutors, the FBI, and the New York Police Department withheld evidence that would likely have led to the acquittal of the two men.

A third man, Mujahid Abdul Halim, 80, confessed to Malcolm X's murder and was released from prison in 2010. Halim claimed during their 1966 trial that Aziz and Islam were innocent.

Malcolm X was shot dead by three gunmen on February 21, 1965, as he prepared to deliver a speech in a Manhattan ballroom.

The review of the case followed the release of a Netflix docuseries called "Who Killed Malcolm X?"