McALESTER, Okla. – As Clayton D. Lockett writhed and groaned on the gurney Tuesday night after a large dose of sedatives had apparently not been fully delivered, the Oklahoma chief of corrections rushed to call the governor and attorney general. Something had gone disastrously wrong with the lethal injection, he told them, and the execution of a second man must be delayed. Gov. Mary Fallin instantly agreed.

On Wednesday, the state faced a domestic outcry and harsh criticism from abroad where anti-death penalty sentiment runs high. The White House weighed in as well, condemning the execution as inhumane. Fallin defended the death penalty but ordered a thorough review of the state’s procedures for lethal injections. She promised an independent autopsy of Lockett, who had been sentenced for shooting a woman and burying her alive, and who died 43 minutes after the initiation of a procedure that was supposed to be quick and painless.

Fallin said the execution of Charles F. Warner, originally also planned for Tuesday, would be delayed until May 13 or later if necessary, but added, “His fellow Oklahomans have sentenced him to death, and we expect that sentence to be carried out as required by law.”

Medical and legal experts said the sequence of events in the Oklahoma State Penitentiary here on Tuesday night raised serious concerns about the methods the state uses for executions and the medical training of those who carry them out.

It was also a stark reminder of the problems with lethal injections, which once seemed to promise a relatively humane, inexpensive way to take lives. There is a history of botched procedures, made worse recently by the unavailability of key drugs and by states’ experimentation with new regimens.

In January, a convict in Ohio gasped for more than 10 minutes while dying, and another Oklahoma inmate cried out, “I feel my whole body burning,” after being injected with drugs from a compounding pharmacy.

At issue in Oklahoma and other states is the secrecy imposed on the sources of lethal drugs, making it impossible for defendants to know whether untested combinations may cause suffering barred by the Constitution.

Groups opposed to the death penalty called for an immediate moratorium on executions in Oklahoma. “In Oklahoma’s haste to conduct a science experiment on two men behind a veil of secrecy, our state has disgraced itself before the nation and world,” said Ryan Kiesel, executive director of the Oklahoma branch of the American Civil Liberties Union.

State officials said the drug cocktail had not been at fault. Rather, they said, the intravenous needles had apparently damaged Lockett’s veins, reducing the amount of drugs entering his bloodstream: the sedative, a paralyzing agent designed to halt breathing, and another agent to stop the heart.

Some experts wondered why an attending doctor had prematurely pronounced Lockett unconscious and how a blown intravenous line could have gone undetected for so long.

On social media, some people said they wished Lockett had suffered more, in keeping with what he did to his victim.

But Jay Carney, the White House press secretary, said the incident had been inhumane.

“We have a fundamental standard in this country that even when the death penalty is justified, it must be carried out humanely,” Carney said, noting that President Obama approved of the death penalty in some circumstances. “And I think everyone would recognize that this case fell short of that standard.”

Tuesday’s events have fanned the embers of concern about lethal injections, which have not turned out to be the cure-all that some had hoped for when Oklahoma, in 1977, was the first state to adopt a three-drug protocol for executions.

“We started with hangings, then moved to electrocution in 1890 and to lethal gas in 1921, with the firing squad always around on the outskirts,” said Deborah W. Denno, a law professor at Fordham University and an expert in the history of lethal injections. “The move to lethal injection in 1977 was an effort to combat all the ills associated with other methods. Nevertheless, we’ve seen botch after botch.”

Incidents of clear suffering have become more common in recent years, Denno said, as states have experimented with new drugs and combinations.

Some advocates of the death penalty have long argued that moving to lethal injections was a mistake. Kent S. Scheidegger, legal director at the Criminal Justice Legal Foundation, which favors the death penalty, said, “I have never liked the idea of medicalizing executions, where we have a procedure now requiring people who perform executions to have medical skills.”

If lethal injections are to continue, a government agency may eventually have to produce the drugs, Scheidegger said, because “the opponents are able to intimidate the private sellers.”

Douglas A. Berman, an expert on sentencing law and policy at Ohio State University, said, “There’s a reasonable modern consensus that death alone should be our maximum punishment, not a torturous death.”

One of the challenges for lethal injections is the scarcity of medical professionals willing to participate. Both the American Medical Association and the American Society of Anesthesiologists say doctors should not take part in executions.