After several denied appeals the US state of Georgia has executed its only female death row inmate despite appeals by her children and Pope Francis to spare her life.

Kelly Renee Gissendaner, 47, died by lethal injection at the state prison in Jackson.

She was convicted of murder in the February 1997 killing of her husband. She conspired with her lover, who stabbed Douglas Gissendaner to death.

Gissendaner was the first woman executed in the state in 70 years.

The United States Supreme court denied Gissendaner three stays of execution on Tuesday.

The Supreme Court of Georgia also denied her a stay of execution and the Georgia Board of Pardons and Paroles declined to grant her clemency after it met earlier on Tuesday to consider new testimony from supporters.

The board did not give a reason for the denial, but said it had carefully considered her request for reconsideration.

Gissendaner was previously scheduled for execution on February 25, but that was delayed because of a threat of winter weather and it was reset for MArch 2.

But corrections officials postponed that execution "out of an abundance of caution" because the execution drug appeared "cloudy".

The parole board, which is the only entity in Georgia authorised to commute a death sentence, also declined to spare Gissendaner's life after a clemency hearing in February.

Her lawyers asked the board to reconsider its decision before the second execution date, but the board stood by its decision to deny clemency.

Gissendaner's lawyers last Thursday submitted a second request to reconsider the denial of clemency, and the board agreed to review new documents and hear from her representatives.

Pope Francis' diplomatic representative in the US, Archbishop Carlo Maria Vigano, on Tuesday sent a letter to the parole board on behalf of the pontiff asking for a commutation of Gissendaner's sentence "to one that would better express both justice and mercy".

He cited an address the pope made to a joint session of Congress last week in which he called for the abolition of the death penalty.

Two of Gissendaner's three children, daughters Dakota and Kayla had asked the board earlier this year to spare their mother's life.

They detailed their own journeys to forgiving her and said they would suffer terribly from having a second parent taken from them.

Her oldest child, Brandon, who had not previously addressed the board, wanted to make a plea for his mother's life, said Susan Casey, a lawyer for Gissendaner.

In the request for reconsideration, Gissendaner's lawyers cited a statement from former Georgia Supreme Court Chief Justice Norman Fletcher, who argued that the death sentence is not proportionate to her role in the crime.

Her lover, Gregory Owen, who did the killing, is serving a life prison sentence and will become eligible for parole in 2022.