Tennessee death row inmate Christa Pike has been taken to hospital after her heart was still beating following two lethal injections during her execution, her lawyer says.
Her legal team filed an emergency motion to halt the convicted murderer's execution as it was happening, saying: "Ms Pike has lost consciousness and still has a heartbeat and is audibly snoring."
One of her attorneys told the BBC that Pike, 50, was "being provided life-saving measures" in hospital after two syringes of pentobarbital had been administered.
Pike was sentenced to death in 1996 for the murder of 19-year-old Colleen Slemmer.
The attempted execution took place at Riverbend Maximum Security Institution in Nashville at about 20:00 local time on Wednesday night.
Pike was given two doses of pentobarbital, and the curtain in the witness room was closed twice, the Associated Press reports.
Media were at some point asked to leave, the news agency said.
Pike's legal team said in a statement to the Tennessean newspaper: "Tonight the State of Tennessee once again failed to carry out a lawful execution.
"We take no pleasure in being right, but the concerns raised by Ms Pike proved to be true: difficult vein access, blown veins, degraded pentobarbital, no emergency medical care available when things inevitably go wrong, all under a protocol that remains veiled in secrecy."
Pike's lawyers filed an emergency motion to stay her execution and administer medical care after the lethal injection was apparently botched.
District Judge Clifton L Corker issued a ruling noting that "medical personnel have begun to administer medical care as requested in the motion".
The Tennessee Department of Correction has said it stands by all the actions it took during the attempted execution.
"The Tennessee Department of Correction followed every step of the State's lawful, established execution protocol approved by the Attorney General's Office," department spokesperson Dorinda Carter told the Tennessean newspaper.
"The lethal injection chemical in the protocol has consistently been effective, and the protocol does not allow for additional procedures beyond what was carried out this evening. Christa Pike has been transported to an off-site medical facility," she said.
Dr Joel Zivot, a professor at the Emory University School of Medicine who told the BBC he had been retained by Pike's legal team as a medical expert, said she likely never achieved a sufficient blood level of pentobarbital to cause apnoea and cardiovascular failure during the attempted execution.
"It's very possible that as a consequence of the delay of the beginning of resuscitation she will have a brain injury," Zivot said in an email.
LIVE Watch: Why was the US execution of Christa Pike halted?
The capital punishment went ahead after the US Supreme Court overturned a reprieve granted by a lower court on Wednesday morning. It was the second time in as many days that the justices gave the go-ahead for Pike's death by lethal injection.
In a ruling earlier in the day, judges from the US Court of Appeals for the Sixth Circuit paused the execution saying they needed more time to consider the arguments in Pike's case.
Her lawyers had argued the jury did not get the chance to weigh mitigating evidence of Pike's documented history of childhood sexual abuse, before they sentenced her to death in 1996.
The defence said that for years, the state of Tennessee had argued in court that she lied about being sexually abused as a child.
But at a recent hearing about her execution method, the state said it did not dispute that she had suffered sexual abuse and rape.
Tennessee's governor denied a clemency request this week from Pike, the only woman on the state's death row.
May Martinez, mother of Colleen Slemmer, outside a court hearing in 2006
Pike was 18 when she and her then-boyfriend, Tadaryl Shipp, beat, tortured and killed 19-year-old Colleen Slemmer, whom they had met at a job training camp for troubled teens.
In her clemency petition, Pike said that she intended to beat Slemmer, not kill her, but that she was unable to "put the brakes on".
"I was a mentally ill 18-year-old kid," she said in a statement. "It took me numerous years to even realise the gravity of what I'd done. Even more to accept how many lives I affected. I took the life of someone's child, sister, friend. It sickens me now to think I had the ability to commit such a crime."
The murder in 1995 created a media frenzy in Knoxville, Tennessee, after Colleen was found with an inverted pentagram - a symbol that is associated with satanic groups - carved into her chest. Pike has denied carving the symbol herself.
Before the killing, Pike had accused Colleen of insulting her and trying to steal her then-boyfriend.
Two other residents at the camp later testified that Pike had bragged about the murder before and after, and showed them a piece of Colleen's skull.
Colleen Slemmer's mother had said she wanted the execution to take place, telling the Associated Press she had waited decades to see Pike's sentence carried out.
"Every time I think about it, I think about Colleen feeling that pain and trying to get up and run," May Martinez told the agency on Saturday.
She said a group helped raise funds for her and her husband to travel from Florida to Tennessee to witness the execution.
"Not a day goes by, or a minute goes by that I do not think about Colleen. Holidays are the worst," Martinez said.
Since 1976, when the Supreme Court resumed the death penalty, only 18 women have been executed in the US, compared to 1,663 men. That's about 1% of all US executions.
Killer Christa Pike to be executed within days - but her defence say she's a victim too
