The U.S. Supreme Court said on Tuesday it would decide whether the commonly used lethal injection method of execution violated the constitutional ban on cruel and unusual punishment. The nation's highest court said it would decide in its upcoming term an appeal by two death row inmates from Kentucky arguing that the three-chemical cocktail used in lethal injections inflicted unnecessary pain and suffering.Their lawyers said the Supreme Court has not addressed the constitutionality of a method of execution or the legal standard used to determine whether the method violated the ban on cruel and unusual punishment in more than 100 years.

All but one of the states with the death penalty and the federal government use lethal injection for executions. The only exception is Nebraska, which requires electrocution.

The standard method involves administering three separate chemicals: sodium pentothal, an anesthetic, which makes the inmate unconscious; pancuronium bromide, which paralyzes all muscles except the heart, and then potassium chloride, which stops the heart, causing death.

Attorneys for the two Kentucky men said at least half of the death row inmates facing imminent execution in the last two years have filed suit challenging the chemicals used in lethal injections. While various lower court federal judges have ruled on the issue, the Supreme Court has yet to decide it.