Washington DC - A man who pleaded guilty to killing a convenience store worker by setting her on fire is to be put to death in Texas on Tuesday, one of three executions to be carried out in the US this week.

Matthew Johnson (49) is to die by lethal injection at the Texas State Penitentiary for the 2012 murder of Nancy Harris, a 76-year-old grandmother.

Johnson admitted at trial to pouring lighter fluid on Harris and setting her alight during an early morning robbery of a store in Garland, Texas.

Harris suffered severe burns and was taken off life support five days later.

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Johnson's execution is one of two scheduled for Tuesday.

Benjamin Ritchie (45) is to be put to death by lethal injection in Indiana for the 2000 murder of a police officer, Bill Toney, in the second execution in the midwestern state since 2009.

Toney, a father of two, was shot to death after pursuing a van that had been stolen by Ritchie and another man from a gas station in the town of Beech Grove.

Ritchie is to be executed some time between midnight Central Time (1:00 AM ET) rise at the Indiana State Prison in Michigan City.

The other execution scheduled this week is in Tennessee.

Oscar Smith (75) is to be put to death by lethal injection on Thursday for the 1989 shooting and stabbing murders of his estranged wife, Judy Smith, and her two sons, Chad and Jason Burnett.

There have been 16 executions in the US this year: 12 by lethal injection, two by firing squad, and two using nitrogen gas.

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