A killer's execution was halted 90 minutes before he was set to die amid arguments from death penalty opponents that the state should wait until the U.S. Supreme Court reviews the constitutionality of lethal injections.

The Nevada Supreme Court issued the last-minute stay Monday for William Castillo, who beat an elderly woman to death with a tire iron.

Castillo, 34, had declined to file appeals of his own and prison officials have said he was ready to die. The American Civil Liberties Union of Nevada appealed to halt any executions in the state.

The U.S. Supreme Court agreed Sept. 25 to review the method of lethal injection used by most states. The high court will hear a challenge early next year from two inmates in Kentucky who claim that lethal injection as practiced by that state amounts to cruel and unusual punishment, in violation of the Eighth Amendment.

Executions in at least 10 states have been halted as a result of the litigation over lethal injections.

The injections, devised as a humane alternative to electrocution and the gas chamber, have come under attack in recent years amid reports that the three-drug cocktail doesn't always work as quickly as intended and that inmates are subjected to excruciating pain.

Nevada prison officials planned to execute Castillo with double doses of three drugs — amounts so strong that the first injection likely would have caused him to immediately become unconscious.

The Nevada high court's ruling came more than two hours after Castillo was served his final meal. The inmate had been slightly sedated as prison staffers prepared to take him to the death chamber.

Nevada Corrections Director Howard Skolnik said Castillo was disappointed when he told him about the stay.

"He asked if it would be possible to get a little more medication to calm him down and take the edge off," the director said.

Two of Berndt's family members had planned to witness the execution, and Skolnik said, "They were hoping for some kind of closure today which they did not get."

Lee Rowland, one of the ACLU lawyers who argued the case Monday before the Supreme Court, welcomed the decision, which was signed by all seven justices.

"Clearly, this was the right thing to do, legally and morally," she said. "We are heartened that this decision will bring Nevada in line with the rest of the country, which has decided to await guidance from the U.S. Supreme Court."

The dispute has not halted executions in all states. Georgia's high court on Tuesday denied a stay of execution for a convicted killer there.

Jack Alderman is scheduled to die by lethal injection Friday. He was sentenced to death for the 1974 slaying of his wife.

The Georgia court noted the U.S. Supreme Court review in its decision.

"If that court stays the execution in this and similar cases in order to consider the issue raised herein, this court will of course comply with that determination and will closely follow every directive from that court," the Georgia order said.

Michael Siem, one of Alderman's lawyers, said Tuesday they would file a state habeas petition, an appeal that could go all the way to the U.S. Supreme Court.

"We're a little surprised based on what's going on in the rest of the country that the Georgia court didn't issue a stay," Siem told The Associated Press.