Washington DC - The US Supreme Court Monday agreed to hear the case of an Oklahoma man convicted of murder, whose story has sparked appeals for clemency from Pope Francis and Hollywood stars.

Richard Glossip (60) had been scheduled to be put to death by lethal injection on May 18, but the nation's highest court put his execution on hold.

The stay came after the Oklahoma attorney general, a Republican, asked the court, in an unusual move, to halt the execution, citing questions about the fairness of his trial.

Following the Supreme Court's Monday announcement that it would hear Glossip's appeal, his lawyer John Mills said his team was "grateful" and emphasized that Glossip had "maintained his innocence throughout a quarter century."

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"Mr Glossip has faced execution nine times, even though the state knew full well that the evidence used to convict him and sentence him to death was false," Mills said.

Glossip was convicted of the 1997 fatal beating of an Oklahoma City motel owner, but has steadfastly maintained his innocence.

Glossip, who worked at the motel, was found guilty of hiring another motel employee, maintenance man Justin Sneed, who was 19 at the time, to carry out the actual murder.

Glossip was convicted based on the testimony of Sneed, who pleaded guilty and was able to negotiate a life sentence, claiming that his co-worker had masterminded the plot.

Actors Mark Ruffalo and Susan Sarandon and British billionaire Richard Branson have been among the celebrities advocating for Glossip's life to be spared.

In 2015, when Glossip's execution also appeared imminent, the representative of Pope Francis in the United States sent a letter on behalf of the pontiff to the then governor of Oklahoma asking that the execution be called off.

His case has also been the subject of a four-episode documentary series titled Killing Richard Glossip.