A court ruled Tuesday that Troy Davis, a death row inmate given a rare second chance by the US Supreme Court, had failed to prove his innocence, clearing the way for his execution.

A highly unusual hearing was ordered in June for Davis, who has been on death row since 1991 for murdering a policeman, because seven of the nine witnesses against him had recanted testimony in the years since his trial.

But a court in the southern US state of Georgia decided on Tuesday that Davis, an African-American, had been unable to show that he was innocent of the fatal shooting of a white police officer in 1989.

"The court concludes that while executing an innocent person would violate the United States Constitution, Mr. Davis has failed to prove his innocence," a judge on the court in Savannah wrote.

Davis's family told AFP it planned to appeal Tuesday's decision.

After a series of failed earlier appeals, the Supreme Court issued a landmark ruling last August, allowing Davis, 41, to present what he claimed was exculpatory evidence that was not reasonably available during his trial.

The highest US court's decision was unusual, in part because it was issued during an official recess, but also because the bar to ordering new consideration of evidence is extremely high.

Davis was sentenced to death for the 1989 Savannah murder of Mark Allen MacPhail. He has always maintained his innocence.

His conviction rested on the testimony of nine witnesses, with no physical evidence such as DNA or fingerprints offered to support his guilt.

But in the years since his trial, seven of the witnesses against him have recanted their testimony, saying they were pressured by police to inculpate Davis.

Even if Davis had proved his innocence, the law was unresolved on whether that would have saved him from the death penalty if his original prosecution did not violate constitutional fair trial standards.

With its racial overtones and Davis's continued claims of innocence, the case has triggered an international outcry, including from the European Union, whose member states oppose the death penalty, as well as from Nobel Peace Prize laureate Desmond Tutu of South Africa, and Pope Benedict XVI.

Anti-execution campaigners from as far away as France and Britain joined US activists at a vigil in June near the courthouse where the hearing was to take place.