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 provide 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".

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.

The attempted capital punishment went ahead after multiple last-minute legal challenges by Pike's lawyers failed.

The US Supreme Court had thwarted two separate efforts to stop the lethal injection.

Late on Wednesday, America's highest court overturned a reprieve granted by a lower court earlier in the day. The lower court had granted a pause, saying it needed more time to consider the arguments in Pike's case.

The Supreme Court had previously dismissed an appeal by Pike's lawyers, who 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.

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