The US Supreme Court Tuesday rejected a prosecution request to reinstate the death penalty for Mumia Abu-Jamal, a former Black Panther convicted of murder whose case has rallied death penalty opponents.

The top US court upheld an appellate decision in April which declared the death sentence for Abu-Jamal unconstitutional.

The justices in 2010 had sent the case back to the lower courts for further review.

Prosecutors had asked the Supreme Court to overturn the appellate decision, which would have allowed for the death penalty to be reinstated for Abu-Jamal, who has been on death row for nearly 30 years and who has claimed he is innocent in the murder of a white police officer.

The Pennsylvania appeals court set aside Abu-Jamal's death sentence over procedural irregularities during his trial, finding that the jury mistakenly had been led to believe that it could not consider mitigating factors against a death sentence.

Abu-Jamal and his supporters claim that the guilty verdict against him was predetermined because he was an African-American and a member of the radical leftist Black Panthers movement.

A writer and president of the Philadelphia Association of Black Journalists at the time of his arrest, he has continued to write from death row.

The NAACP Legal Defense & Educational Fund said the decision marks the fourth time that the federal courts have found that Abu-Jamal's sentencing jury was misled about the constitutionally mandated process for considering evidence supporting a life sentence.

"At long last, the profoundly troubling prospect of Mr. Abu-Jamal facing an execution that was produced by an unfair and unreliable penalty phase has been eliminated," said John Payton of the NAACP.

"Like all Americans, Mr. Abu-Jamal was entitled to a proper proceeding that takes into account the many substantial reasons why death was an inappropriate sentence."