The United States executed Thursday an Oklahoma prisoner convicted of murdering a three-year-old boy, but an Alabama prisoner was temporarily spared the lethal injection after a legal back-and-forth meant officials ran out of time.

The Oklahoma execution brought to three the number of inmates executed in two days, after prisoners received lethal injections in Arizona and Texas on Wednesday night.

After a pause during the pandemic, the rate of executions in the United States has picked up this year, especially in conservative southern states.

Richard Fairchild, 63, was killed by lethal injection Thursday morning in the Oklahoma State Penitentiary in McAlester.

He became the seventh inmate to be executed since the state resumed capital punishment in October 2021 after a six-year pause due to a series of botched executions.

Fairchild was sentenced to death 26 years ago for burning, beating, and killing his girlfriend's son.

Witnesses to the execution said he expressed remorse and apologized to the victim's family.

In Alabama, the execution of 57-year-old Kenneth Smith was set for 6:00 pm (0200 GMT), despite controversy over his sentence.

Smith's lawyers filed a final appeal Wednesday with the Supreme Court, but its conservative majority rejected a stay.

That meant officials were cleared to carry out the execution from about 10 pm, with two hours before the inmate's death warrant expired, Alabama Department of Corrections commissioner John Q. Hamm told reporters.

"At approximately 11.21 pm, we called off the execution," he said, adding that it was judged unlikely they could complete the process before the death warrant expired.

In 1988, a man hired Smith, alongside another hitman, to kill his wife and make it look like a burglary.

The husband killed himself a week after the murder and police focused on the two assassins.

Smith was sentenced to death, but an appeals court overturned the ruling and called for a fresh trial.

He was again convicted in 1996, but the jurors were divided over the sentence, and 11 out of 12 recommended a life sentence.

The judge overrode the jury and imposed the death sentence, a legal move that is now banned across the United States.