McAlester, Oklahoma - An Oklahoma man convicted of killing a woman during a home robbery was put to death by lethal injection on Thursday, the third execution in the US this week.

Wendell Grissom (56) was sentenced to death for the 2005 murder of Amber Matthews (23), who was shot in the head while trying to protect a friend's two young daughters.

Grissom was pronounced dead 10 minutes after the execution process began at the state penitentiary in McAlester, the Oklahoma Department of Corrections said in a statement.

It said the execution was carried out using a three-drug protocol: Midazolam, which causes sedation, Vecuronium Bromide, which halts respiration, and Potassium Chloride, which stops the heart.

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According to court documents, Grissom, a truck driver, and another man, Jessie Johns, broke into the home of Dreu Kopf, a friend of Matthews, with the intention of committing a robbery.

Grissom shot and wounded Kopf and killed Matthews while she was hiding in a bedroom in an attempt to shield Kopf's two children.

Johns was sentenced to life in prison without parole.

There have been three executions in the US this week, and a fourth – in Florida – is scheduled for later on Thursday.