Washington, Aug 6 (IANS): An American man convicted of mass murder was executed in Florida, after his appeals over mental illness were finally rejected, media reports said.

John Errol Ferguson, 65, was executed at the Florida State Prison by a lethal injection, in front of about two dozens of witnesses including some family members of the eight victims murdered by him in the 1970s.

The execution was carried out Monday night, hours after the US Supreme Court denied the final request for a stay by Ferguson's attorneys, who argued that Ferguson was mentally ill and his execution would be a cruel and unusual punishment, Xinhua reported.

Ferguson, together with two others, was convicted of murdering six people in July 1977 during a robbery at a house in Carol city. He was also convicted of killing a 17-year-old couple in 1978 during another robbery, in which he also raped the female victim.

Ferguson was arrested in April 1978 for the first murder case, and he later confessed to the killing of the young couple. He was sentenced to death in both cases.

He was once scheduled to be executed last October after the Florida Supreme Court held a lower court ruling based on testimony by a team of psychiatrists who determined he "understands what is taking place and why".

But the execution was blocked in the final hours by the 11th US Circuit Court of Appeals after Ferguson's lawyers appealed again on his mental illness.