Miami, Florida - An Alabama man who murdered his girlfriend is to be put to death by nitrogen gas on Tuesday, one of at least three executions to be carried out in the US this week.

Gregory Hunt (65) was convicted of the 1988 rape and murder of 32-year-old Karen Lane, whom he had been dating for a month.

Hunt is to be executed by nitrogen hypoxia, which involves pumping nitrogen gas into a facemask, causing the prisoner to suffocate.

The execution is to be carried out at 7:00 PM ET at the Alabama state prison in Atmore.

Law enforcement LAPD shoots reporter with rubber bullets amid LA immigration protests

It will be the fifth execution in the state using nitrogen gas, which has been denounced by UN experts as cruel and inhumane.

Only one other state, Louisiana, has used this method.

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

Anthony Wainwright (54) is to be put to death by lethal injection at 6:00 PM ET at the Florida state prison in Raiford.

Wainwright was convicted of the 1994 rape and murder of Carmen Gayheart, a 23-year-old nursing student and mother of two young children.

Wainwright and an accomplice, Richard Hamilton, abducted Gayheart three days after escaping from a prison in North Carolina.

Hamilton was also sentenced to death for Gayheart's murder, but died in prison.

A third execution this week is scheduled to take place on Thursday in Oklahoma, where John Hanson (61) is to be put to death for the 1999 kidnapping and murder of Mary Bowles (77).

Hanson's execution has been temporarily put on hold by a judge amid claims his rights were violated during a clemency hearing.

Oklahoma Attorney General Gentner Drummond has asked an appeals court to lift the stay to allow the execution to go ahead.

The fourth execution this week is to be carried out in South Carolina, where Stephen Stanko (57) is to be put to death by lethal injection.

Stanko was convicted of the 2005 murders of his girlfriend, 43-year-old Laura Ling, and Henry Turner, a 74-year-old friend.

There have been 19 executions in the US this year: 15 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.

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