Media playback is unsupported on your device Media caption Amnesty International's Laura Moye: "Serious doubts about his guilt remain"

The US state of Georgia has rejected a final clemency appeal for Troy Davis on the eve of his execution for the 1989 murder of an off-duty policeman.

The Georgia Board of Pardons and Paroles made its decision after hearing testimony from the victim's family, Davis' supporters and prosecutors.

He was sentenced in 1991 for killing Mark MacPhail but most of the witnesses have since changed their testimony.

Davis, 42, is due to face a lethal injection on Wednesday.

Defence lawyers said the appeal to the pardons board was the last option for Davis, who has been scheduled for execution four times in the past four years.

His legal team said in a statement they were "incredibly disappointed" by the decision as the prosecution's case "cannot resolve the significant, lingering doubts that exist here".

'Truth finally heard'

They called on District Attorney Larry Chisolm to vacate the death warrant and for the pardons board to reconsider their decision immediately.

Image caption Some 300 rallies, vigils and events for Troy Davis have occurred worldwide

Prosecutors insist they have no doubt that they charged the right person with the crime.

MacPhail's relatives were relieved at the parole board decision.

"Justice was finally served for my father," said Mark MacPhail Jr, the victim's son. "The truth was finally heard."

But Amnesty International, which has supported Davis in his wrongful conviction claim, called the decision "unconscionable".

Its USA director, Larry Cox, said in a statement: "Should Troy Davis be executed, Georgia may well have executed an innocent man and in so doing discredited the justice system."

Amnesty International and the National Association for the Advancement of Colored People plan a demonstration in support of Davis on Tuesday evening.

Reverend Al Sharpton plans a midday vigil at the state prison in Jackson on Wednesday.

More than one million people worldwide have signed petitions for clemency in his case.

Pope Benedict XVI, former US President Jimmy Carter and EU foreign policy chief Catherine Ashton are among those who have backed Davis, who has always maintained he is innocent.

His guilt has been questioned because seven of nine witnesses who helped convict him during the original trial have either changed their testimony or recanted.

No murder weapon was ever found and no DNA evidence or fingerprints conclusively linked Davis to the shooting.

At a rare 2010 innocence hearing - ordered by the US Supreme Court - two witnesses said they falsely incriminated Davis, while two others told the court another had confessed to being the actual killer.

US District Court Judge William T Moore Jr said there was not enough evidence to vindicate Davis or grant him a new trial.

Federal appeals courts and the Georgia Supreme Court have upheld Davis' conviction.