Washington DC - A South Carolina man convicted of murdering his ex-girlfriend's parents has chosen to be put to death by firing squad next month in what would be the first such execution in the US since 2010.

Brad Sigmon (67) is to be executed on March 7 at a prison in Columbia, the South Carolina capital, for the 2001 murders of David and Gladys Larke, who were beaten to death with a baseball bat.

Sigmon had a choice between lethal injection, firing squad, or the electric chair as his manner of execution.

Gerald "Bo" King, one of his lawyers, said Sigmon had chosen the firing squad after being placed in an "impossible" position, forced to make an "abjectly cruel" decision about how he would die.

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"Unless he elected lethal injection or the firing squad, he would die in South Carolina's ancient electric chair, which would burn and cook him alive," King said in a statement.

"But the alternative is just as monstrous," he said. "If he chose lethal injection, he risked the prolonged death suffered by all three of the men South Carolina has executed since September."

Sigmon, if the execution goes ahead, would be the first person ever executed by firing squad in South Carolina.

The last US firing squad execution was in Utah in 2010. Two others have also been carried out by firing squad in Utah – in 1996 and in 1977.

According to the South Carolina Department of Corrections (SCDC), the death chamber at the prison where Sigmon is to be executed has been renovated to accommodate a firing squad.

Bullet-resistant glass has been placed between the witness room and the death chamber.

The inmate will be restrained in a metal chair with a hood over his head 15 feet away from a wall with a rectangular opening, the SCDC said.

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A three-person firing squad of SCDC volunteers armed with rifles will fire through the opening in the wall.

All three rifles will have live ammunition.

An "aim point" will be placed above the inmate's heart by a member of the execution team, the SCDC said.

There have been five executions in the US this year and there were 25 last year.

The death penalty has been abolished in 23 of the 50 US states, while three others – California, Oregon, and Pennsylvania – have moratoriums in place.

Three states – Arizona, Ohio, and Tennessee – that had paused executions have recently announced plans to resume them.

President Donald Trump is a proponent of capital punishment and on his first day in the White House he called for an expansion of its use "for the vilest crimes."