Two US states plan executions the same day
Death row inmates Oscar Franklin Smith (L), and Carl Buntion, both of whom were scheduled to be executed(AFP)

Texas and Tennessee prepared Thursday to execute their oldest Death Row inmates, men in their 70s who were both convicted of murder.

In Texas, lawyers for Carl Buntion, 78 and convicted of killing a policeman more than 30 years ago, have filed a final appeal to the US Supreme Court seeking a stay. If it is rejected he will be executed by lethal injection in the early evening.

Tennessee for its part planned to execute Oscar Franklin Smith, 72, by lethal injection for killing his estranged wife and her two teenage sons in 1989.

Buntion, who does not dispute his guilt, is the oldest man on Death Row in Texas, the conservative southern state which puts more prisoners to death than any other American state.

His lawyers have argued that executing him now, so many years after his crime, would constitute "cruel and unusual punishment," which is banned under the US constitution.

Texas law also requires it be established that Buntion would likely harm others if he is not executed, his lawyers said.

Buntion, they said, poses no danger to anyone and suffers from multiple ailments including arthritis, vertigo, hepatitis, sciatic nerve pain and cirrhosis.

"Mr. Buntion is a frail, elderly man," his lawyers said in a petition to the Texas Board of Pardons and Parole, "and will not be a threat to anyone in prison if his sentence is reduced to a lesser penalty."

Buntion has also been in solitary confinement for the past 20 years, restricted to his cell for 23 hours a day.

In June 1990, he shot and killed a Houston police officer during a routine traffic stop.

At that point he already had a long criminal record and was out on parole after a conviction for sexually assaulting a minor.

In 1991 Buntion was sentenced to death. The sentence was vacated in 2009 by the state's highest court but three years later another jury reinstated it.

Last year the US Supreme Court declined to issue a stay of execution for Buntion.