Oklahoma's Supreme Court has ruled that two death row inmates are not entitled to know the source of the drugs that will be used to kill them.

In rejecting the inmates' claims, the court also lifted a stay of execution that it had granted earlier in the week in a case that placed Oklahoma's two highest courts at odds and prompted calls for impeaching justices on the Supreme Court.

Wednesday's decision paves the way for death row inmates Clayton Lockett and Charles Warner to receive a lethal injection at the Oklahoma State Penitentiary in McAlester.

A stay of execution issued on Tuesday by Gov. Mary Fallin remains in place for Lockett, but only until April 29, the same day Warner is scheduled to die.

Fallin's spokesman Alex Weintz has said the governor is still reviewing the court's ruling and has not made a decision on what she will do. Weintz has said it is possible both men could be executed on April 29, the AP news agency reported.

Diane Clay, a spokeswoman for Oklahoma Attorney General Scott Pruitt, said the court's decision affirmed a long-standing precedent that the source of the execution drugs should remain confidential to avoid "intimidation used by defence counsel and other anti-death penalty groups."

"These death row inmates have not contested their guilt for murdering two innocent victims nor have they contested their sentences of death," Clay said. "The legal wrangling of the attorneys for Lockett and Warner has served only to delay their punishment for the heinous crimes they committed."

The nine-member Oklahoma Supreme Court caused an uproar on Monday when it issued a 5-4 opinion that delayed the executions until the inmates' claims over drug-source secrecy were handled.

The justices provoked some in the Republican-controlled legislature to such an extent that one member ordered articles of impeachment be drafted, saying on Wednesday that the judges violated their oaths of office and engaged in a "wilful neglect of duty."

On Wednesday, the justices reversed a lower court decision that said preventing the inmates from seeking information about the drugs used in lethal injections violated their rights under the state constitution.

The high court said the inmates' constitutional rights were not violated by keeping the drug sources secret.

Source: Agencies