JACKSON, Ga. (AP) — Georgia postponed its first execution of a woman in 70 years late Monday because of concerns about the drug to be used in the lethal injection.

The pentobarbital was sent to an independent lab to check its potency and the test came back at an acceptable level, but during subsequent checks it appeared cloudy, Georgia Department of Corrections spokeswoman Gwendolyn Hogan said. Corrections officials called the pharmacist and decided to postpone the execution "out of an abundance of caution," she said. No new date was given.

Pentobarbital is the only drug used in Georgia executions. For other recent executions, the state has gotten the drug from a compounding pharmacy, but officials did not immediately respond late Monday when asked if that was the source in this case. Georgia law prohibits the release of any identifying information about the source of execution drugs or any entity involved in an execution.

Kelly Renee Gissendaner was scheduled to be executed at 7 p.m. at the prison in Jackson for the February 1997 slaying of her husband, Douglas Gissendaner. The execution was put on hold while officials waited for the U.S. Supreme Court to either grant or deny a stay requested by her lawyers. The court had still not ruled more than five hours later.

Her lawyers were seeking a delay pending a U.S. Supreme Court ruling in another case out of Oklahoma, and an appellate court had rejected that request. Late Monday, the lawyers added additional arguments for the high court: that it should consider a stay because Gissendaner didn't kill her husband, Douglas Gissendaner, herself in February 1997. They also argued that she had been thoroughly rehabilitated.

Previously, courts had found Gissendaner had plotted the stabbing death of her husband by her boyfriend, Gregory Owen, who will be up for parole in eight years after accepting a life sentence and testifying against her.

Gissendaner would have been only the 16th woman put to death nationwide since the Supreme Court allowed the death penalty to resume in 1976. About 1,400 men have been executed since then, according to the Death Penalty Information Center.

The Georgia Board of Pardons and Paroles, the only entity authorized to commute a death sentence, denied clemency last week and upheld that decision late Monday. Gissendaner's lawyers had urged the board to reconsider and "bestow mercy" by commuting her sentence to life without parole. The board said it voted to abide by its earlier decision after "careful consideration" of the request.

Kelly and Douglas Gissendaner had a troubled relationship, repeatedly splitting up and getting back together, divorcing and remarrying. At the time of her husband's death, Gissendaner was a 28-year-old mother of three children, 12, 7 and 5 years old. And she had an on-again, off-again lover in Owen.

Rather than divorcing her husband again, Gissendaner repeatedly pushed Owen to kill him, prosecutors said. Acting on her instructions, Owen ambushed her husband while she went out with friends, and forced him to drive to a remote area. Then he marched him into the woods and stabbed him multiple times, prosecutors said.

Owen and Gissendaner then met up and set fire to the dead man's car in an attempted cover-up. Both initially denied involvement, but Owen eventually confessed and testified against his former girlfriend.

Her lawyers challenged the constitutionality of her sentence as disproportionate, given that she wasn't there when Owen killed her husband, and yet Owen will eventually be eligible for parole. But Georgia's Supreme Court voted 5-2 Monday to deny her motion, citing Owen's testimony that she pushed for murder rather than divorce so that she could get her husband's insurance money.

In their request Monday for reconsideration, Gissendaner's lawyers said the parole board did not have a chance to hear the overwhelmingly positive testimony of many corrections employees who declined to speak up for fear of retaliation.

Her clemency petition already included testimonials from dozens of spiritual advisers, inmates and prison staff who described a seriously damaged woman transformed through faith behind bars. She has shown remorse and provided hope to struggling inmates while helping guards maintain control, they said.

"The spiritual transformation and depth of faith that Ms. Gissendaner demonstrates and practices is a deep and sincere expression of a personal relationship with God," Prison chaplain Susan Bishop wrote. "It is not a superficial religious experience."

Two of Gissendaner's three children also asked the board to spare their mother's life, describing their own emotional journey from anger and bitterness to forgiveness.

"The impact of losing my mother would be devastating. I can't fathom losing another parent," wrote her daughter, Kayla Gissendaner. "My mom has touched so many lives. Executing her doesn't bring justice or peace to me or to anyone."

But it also has been "a long, hard, heartbreaking road" for Douglas Gissendaner's parents and sister, according to a statement from them issued through the Gwinnett County district attorney's office. The family made it clear they wanted the execution to go forward.

Several dozen people gathered outside the prison in support of Gissendaner, including some women who served time with her.

Kara Tragesser recalled Gissendaner telling her "You can do better!" when she was put on lockdown while serving a 10-year sentence for armed robbery.

"We're here because Kelly's made a difference in our lives," Tragesser said.

Michelle Collins, who did time for forgery, remembered Gissendaner persuading her to stop misbehaving and start caring about her future.

"She looked around at us and said, 'At least y'all are going to get out of here again. Who are you to throw your lives away when I'm never going to get out of here?'" said Collins.

"She gave me the will to do something good when I got out," said Collins, adding that she now makes good money working for a Fortune 500 company. "She told me to make sure I never came back and I never have."

A loud cheer came up from the crowd gathered outside the prison when they heard the execution had been postponed.