A U.S. court halted the execution of a man convicted of the rape and murder of an 11-year-old boy in a step widely expected as the U.S. Supreme Court hears a constitutional challenge to the use of lethal injections.

The U.S. District Court's stay in Mark Dean Schwab's execution, scheduled for Thursday, continued the move to halt death sentences in the United States pending an appeal to the high court by two inmates in the state of Kentucky who contend the toxic three-drug combination used for lethal injections there is cruel and unusual punishment.

Florida uses the same drugs, and Schwab's appeal was based on the same constitutional grounds.

The state quickly filed an appeal seeking to overturn the order.

The stay will remain in effect while the high court considers the Kentucky cases. The U.S. Supreme Court has delayed executions in three other states while it considers the appeals of the Kentucky inmates.

Schwab's execution for the 1991 killing of Junny Rios-Martinez was to be the first in Florida since the botched execution of Angel Diaz last Dec. 13. It took 34 minutes for Diaz to die — twice as long as normal — because the guards pushed the needles through his veins.

The execution sparked outrage among death penalty opponents and prompted then-Governor Jeb Bush, President George W. Bush's brother, to suspend executions in the state. Officials then revised the procedure and Governor Charlie Crist lifted the moratorium by signing Schwab's death warrant.

In its response to Schwab's appeal, the state of Florida said the state's procedure is designed to prevent potentially painful drugs from being injected until an inmate is "deeply unconscious."

Crist, issued a statement, saying, "I am disappointed that the family of the victim, Junny Rios-Martinez, will have to continue to wait to see justice done."

Schwab, who had an earlier sexual assault conviction, saw the boy's photo in a newspaper and gained the confidence of his family, claiming he was with the newspaper and was writing an article on him.

Schwab later called Junny's school and pretended to be Junny's father and asked that the boy meet him. A friend saw Junny get into a truck with a man.

During his trial, it was revealed that Schwab kidnapped the boy, bound his hands and face with duct tape and cut off the boy's clothes. He raped the crying boy before strangling him.

After the boy's murder, the Legislature passed the Junny Rios-Martinez Act, which prohibits sex offenders from early release from prison.