Media playback is unsupported on your device Media caption Witnesses at his death said Davis was defiant in proclaiming his innocence to the end

Death row inmate Troy Davis has had his final appeal rejected by the US Supreme Court as he awaits execution for the murder of a policeman.

The state of Georgia's top court earlier also rejected an appeal by the 42-year-old, whose lethal injection was scheduled for 19:00 EST (23:00 GMT).

Seven out of nine witnesses recanted their testimony in the case. Protests and vigils have been held all week.

Davis' request for a polygraph test was denied by prison officials.

He was convicted in 1991 of killing Mark MacPhail, an off-duty police officer, but maintains he is innocent.

The US Supreme Court judges took more than four hours to issue their rejection of the final appeal, an unusually long time for such a ruling.

"The application for stay of execution of sentence of death presented to Justice [Clarence] Thomas and by him referred to the Court is denied," it read.

Ballistic 'flawed'

MacPhail was shot dead in July 1989 as he tried to help a homeless man who was being attacked in a Burger King car park.

Image caption Mark MacPhail was shot dead in 1989 as he tried to defend a homeless man

Prosecutors say Davis was beating the man with a gun after demanding a beer from him.

But no gun was ever found and no DNA evidence conclusively linked Davis to the murder.

On Wednesday morning, Davis' lawyers appealed to the county court responsible for Georgia's death row, but that was also rejected.

The legal team had argued that ballistic testing from the case was flawed.

The pardons board also dismissed an appeal to reconsider their decision on Monday to deny Davis clemency.

During what could be his last hours, Davis had not asked for a final meal and was spending time with family, friends and supporters.

'It has got to end'

Prosecutors say they have no doubts as to his guilt.

"He had all the chances in the world," Anneliese MacPhail, the mother of the murdered policeman, said in a phone interview with the Associated Press news agency.

"It has got to come to an end."

But Davis counts among his supporters Pope Benedict XVI and former US President Jimmy Carter, as well as US conservative figures like representative Bob Barr and former FBI director William Sessions.

Media playback is unsupported on your device Media caption Bianca Jagger says the evidence against Mr Davis is virtually non-existent

Spencer Lawton, the district attorney who secured the conviction, told the Associated Press news agency he was embarrassed that the execution had taken so long.

"What we have had is a manufactured appearance of doubt which has taken on the quality of legitimate doubt itself. And all of it is exquisitely unfair," he said.

Outside the prison in Jackson, Georgia - where Davis is to be executed - a crowd of about 200 people have gathered, chanting "They say death row; we say, hell no!"

Around 10 counter-demonstrators were also present, voicing support for the death penalty and for the family of MacPhail.

His sister Martina Correia told reporters: "Troy Davis has impacted the world. They say, 'I am Troy Davis,' in languages he can't speak."

There is a heavy police presence outside the prison, including large numbers of riot police, but no disturbances have been reported.

Protests in Paris

Davis' conviction has been upheld by several federal and appeal courts.

He was previously denied a hearing at the US Supreme Court after a federal judge refused a new trial for his case.

Image caption Protests in Georgia have been organized by the Amnesty International and NAACP

Davis' execution date has been stopped three times.

While vigils have been scheduled at both the Georgia state capitol and the jail, protests have taken on an international dimension since Monday's decision to deny clemency.

The Council of Europe has called for Davis' sentence to be commuted.

Amnesty International and other groups organised protests at the US embassy in Paris, where 150 people gathered in Place de la Concorde, holding signs bearing Davis' image.

In Washington DC dozens gathered outside the White House, in the hope that President Barack Obama might intervene at the last-minute.

Reports suggest around a dozen people have been arrested for refusing to co-operate with police.

But White House press secretary Jay Carney said it would not be appropriate for the president to interfere in specific cases of state prosecution, such as this one.

The president does not have the authority to pardon Davis, but he could order an investigation into the case and delay the execution.

Meanwhile in the US state of Texas another death row inmate, Lawrence Russell Brewer, was executed on Wednesday evening - in a very different case.

In 1998, white supremacist gang member Brewer, 44, dragged a black man chained to the back of a pick-up truck along a road until he died.