WASHINGTON - The US Supreme Court Monday did not rule on whether it would hear arguments in the case of an African-American granted an 11th hour stay of execution for the murder of a white police officer.

The execution of Troy Davis, 39, who has spent 17 years on death row in Georgia, was dramatically halted two hours before he was due to die late last month amid growing doubts about his conviction.

Defense lawyers have asked the Supreme Court to rule on the constitutionality of executing a person when there is new, substantial evidence to show he was not guilty of the crime.

Seven out of nine witnesses who gave evidence at Davis' trial have recanted or changed their testimony that he murdered policeman, Mark MacPhail.

The witnesses said statements implicating Davis had been coerced by strongarm police tactics, challenging the backbone of the prosecution's case in the absence of any weapon, fingerprints and DNA linking him to the murder.

Davis was originally sentenced to die in July last year, but he was granted a last-minute stay of execution then by the Georgia Board of Pardons and Parole.

Earlier in September, however, the parole board issued a decision denying Davis clemency which was confirmed by the Georgia supreme court.

International figures including former US president Jimmy Carter, Nobel Peace Prize winner Desmond Tutu of South Africa and Pope Benedict XVI have spoken out against Davis's execution.

In a statement Carter said last month: "Executing Troy Davis without a real examination of potentially exonerating evidence risks taking the life of an innocent man and would be a grave miscarriage of justice."

The case has also been taken up by Amnesty International and a group known as Georgians for Alternatives to the Death Penalty (GFADP).

The group's chairwoman Sarah Totonchi said on September 23: "Certainly we know that across the spectrum in the death penalty when the defendant is black and the victim is white, the likelihood of the death penalty being imposed is much greater.

"When the person is a white cop, the defendant has almost no chance."