A man convicted of forging cheques belonging to his mother's friend and killing the man after he demanded money back has been executed, officials said.

The execution of Brian Keith Terrell, 47, was carried out at earlier on Wednesday at the Georgia state prison in Jackson, the Department of Corrections said.

Terrell was convicted of murder in the June 1992 killing of 70-year-old John Watson of Covington, a community east of Atlanta.

Terrell was on parole in 1992 when he stole 10 of Mr Watson's cheques and signed his name on some, prosecutors said.

Mr Watson told police about the theft but asked them not to pursue charges if most of the money was returned.

The day he was to return the money, according to the prosecutors, Terrell had his cousin drive him to Mr Watson's house where he shot the victim multiple times.

Terrell's lawyers had said their client was innocent.

They argued that no physical evidence connected Terrell to the killing and that prosecutors had used false and misleading evidence to secure the conviction that drew the death penalty. State lawyers countered that the courts had already heard and rejected the defence arguments.

The US Supreme Court, without explanation, denied a request for a stay about four hours after the 7pm scheduled execution time.

On Monday, the Georgia Board of Pardons and Paroles had denied Terrell's request for clemency.

A state court on Tuesday dismissed a complaint in which Terrell claimed innocence, and the state Supreme Court declined to halt the execution.

Terrell also had filed a court challenge saying the state cannot ensure the safety or efficacy of the drug it plans to use to execute him.

A federal court on Tuesday rejected that challenge, and Terrell appealed to the 11th US Court of Appeals.

Terrell was previously set for execution on March 10, but after Department of Corrections officials discovered solid chunks had formed in the drug that was to be used in another execution on March 2, they temporarily suspended all executions to allow time for an analysis of the drug.

The state has said the most likely cause was that the drug was shipped and stored at a temperature that was too cold. The state has taken precautions to prevent that from happening again, state lawyers have said.