US death row inmate Christa Pike is “conscious and speaking” after surviving a failed execution attempt in the US state of Tennessee last week, her lawyers say.

Pike, 50, continues to receive critical medical care while handcuffed in hospital, according to a statement from her attorneys on Tuesday.

She was sentenced to death following her conviction for murdering Colleen Slemmer in 1995. But Pike survived two lethal injections last Wednesday and was transferred to a hospital in Nashville for treatment.

Her lawyers had said in the days afterwards that she was unconscious while medical staff cleared her body of the pentobarbital injected during the execution attempt.

Pike’s lawyers said on Tuesday that her recovery is “medically unprecedented”, and while her prognosis remains unclear, “at a minimum, we expect a long recovery”.

They said she is the only person known to have survived a completed execution attempt in the US.

Deborah Denno, a criminologist and professor at Fordham Law School, said she was “absolutely astonished” that Pike is conscious and speaking.

There were seven other cases where prisoners survived slated executions, but in those cases, executioners were not able to inject anything into the inmates’ veins, Denno told the BBC.

Pike “is the only person for whom some kind of toxin has been injected,” she said.

“They did everything they were supposed to do as part of the execution process, and it simply didn’t work,” Denno said. “This has never happened before.”

Authorities have not yet said whether they will try again to execute Pike. They have also not offered an explanation for what went wrong.

Tennessee Governor Bill Lee suspended all executions for the rest of the year – and the head of prisons in the state said over the weekend that he plans to resign.

Pike was 18 when she and her then-boyfriend, Tadaryl Shipp, beat, tortured and killed 19-year-old Slemmer, whom they had met at a job training camp for troubled teens.