America's death penalty debate raged Thursday after it took nearly two hours for Arizona to execute a prisoner who lost a Supreme Court battle challenging the experimental lethal drug cocktail.

Convicted killer Joseph Wood gasped and snorted during the 117 minutes it took him to die Wednesday after he was injected with a relatively untested combination of the sedative midazolam and painkiller hydromorphone, witnesses and his lawyers said.

It usually takes 10 minutes to put an inmate to death using a lethal injection.

It was the second botched execution in the United States so far this year, prompting outrage from death penalty abolitionists and critics.

"He gasped and struggled to breathe," attorney Dale Baich said after the execution in the southwestern US state.

So drawn out was the procedure that Wood's lawyers fielded an emergency motion during the execution to try to cut it short and revive their client.

Wood, who was convicted for the 1989 murders of his girlfriend Debbie Dietz and her father Gene, finally died at 3:49 pm (2249 GMT).

But the victims' family rejected claims that Wood had died an agonizing death.

"You don't know what excruciating is. What's excruciating is seeing your dad lying there in a pool of blood, seeing your sister lying there in a pool of blood," Jeanne Brown told reporters.

"That's excruciating. This man deserved it. I don't believe he was gasping for air. I don't believe he was suffering. Sounded to me as though he was snoring."

- 'Bungled' execution -

"Arizona appears to have joined several other states who have been responsible for an entirely preventable horror -- a bungled execution," Baich said in a statement.

Just a day before he was finally put to death, the US Supreme Court had denied Wood's request to halt the execution because of the state's secrecy over the nature and origin of the drug cocktail.

Witness Michael Kiefer, a reporter for The Arizona Republic, said Wood gasped more than 640 times.

"It was very disturbing to watch... At a certain point, you wondered if he was ever going to die," local Fox News affiliate news anchor Troy Hayden said.

But witnesses and medical observers said Wood did not suffer.

Capital punishment opponents vowed to redouble their efforts to outlaw the practice, which already has been abandoned in most other countries.

"The worst part about Joseph Wood's botched execution was, it was entirely predictable and avoidable," said National Coalition to Abolish the Death Penalty executive director Diann Rust-Tierney.

"Americans have had enough of the barbarism. We're learning, sadly, that in too many cases, we are simply incapable of carrying out capital punishment in the humane way in which our laws guarantee."

She noted that the lethal drug cocktail used in Wood's execution had only been used once before, in Ohio, where it took inmate Dennis McGuire 26 minutes to die.

Arizona Governor Jan Brewer said she was concerned about the time it took for Wood to be executed, and ordered a "full review" of the process.

"One thing is certain, however, inmate Wood died in a lawful manner and by eyewitness and medical accounts he did not suffer," she insisted.

"This is in stark comparison to the gruesome, vicious suffering that he inflicted on his two victims -- and the lifetime of suffering he has caused their family."

- Failed court challenge -

Wood was one of several inmates to resort to the courts to seek greater transparency about the method being used to put them to death, amid concern about the efficacy of the lethal drug protocol.

Outrage grew after another execution went awry in Oklahoma in April, with the inmate appearing to suffer before he died.

Oklahoma suspended its executions for six months after putting to death convicted killer and rapist Clayton Lockett in a process that took 43 minutes.

Individual US states may choose whether or not they will implement the death penalty.

Those that carry out executions have relied increasingly on compounding pharmacies, which lack federal approval, since European drugmakers refused to provide products used to execute inmates.

Wednesday's execution was the 26th in the United States, and the first in Arizona since October.