Washington DC - Two men on death row were to be executed Tuesday in the US, including a Black man convicted of murder whose conviction has been described as a "devastating miscarriage of justice."

Marcellus Williams (55) was sentenced to death in Missouri for the 1998 killing of Felicia Gayle, a former newspaper reporter.

Travis Mullis (38) is to be put to death by lethal injection in Huntsville, Texas, for stomping his three-month-old son, Alijah Mullis, to death in 2008.

Pending any last-minute interventions, both men will be put to death by lethal injection, raising the total number of US executions this year to 16.

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Williams has insisted he is innocent, and the NAACP civil rights group has urged Governor Michael Parson to stay his execution.

Parson on Tuesday said that Williams's execution in Missouri would go ahead despite protests, including by British billionaire Richard Branson, who bought a full-page advert in the Kansas City Star newspaper decrying a "devastating miscarriage of justice."

"No jury nor court, including at the trial, appellate, and Supreme Court levels, have ever found merit in Mr. Williams's innocence claim. At the end of the day, his guilty verdict and sentence of capital punishment were upheld," Parson said in a statement.

Felicia Gayle was found dead at her St. Louis home in Missouri, stabbed 43 times by a kitchen knife during what appeared to be a burglary gone wrong.

Williams, who had previous convictions for burglary and robbery, was convicted on the testimony of a former jail cellmate and an ex-girlfriend, though his DNA was not found on the knife or at the crime scene.

His execution was stayed by the Missouri Supreme Court in 2015, and again by the state's then-governor Eric Greitens in 2017, following the discovery of male DNA on the knife that did not match Williams.

This year, local prosecutors initiated proceedings to overturn his conviction. However, on Monday, the state Supreme Court ruled in a unanimous decision that it would not stop Williams's execution.

The death penalty has been abolished in 23 states, while six others – Arizona, California, Ohio, Oregon, Pennsylvania and Tennessee – have moratoriums in place.