Oklahoma does not have all of the lethal drugs necessary to carry out an execution set for this week, the state attorney general said Monday, and the prisons agency says a quirk in the law prevents the state from switching to electrocution or firing squad.

Despite the drug shortage, lawyers for the state are fighting an attempt by two inmates to delay their executions as the condemned men seek more information about Oklahoma's execution procedures.

Assistant Attorney General Seth Branham says the Oklahoma Department of Corrections is attempting to obtain suitable execution drugs.

"This has been nothing short of a Herculean effort, undertaken with the sole objective of carrying out ODOC's duty under Oklahoma law to conduct Appellants' executions," Branham wrote in a brief to the Oklahoma Court of Criminal Appeals filed Monday. "Sadly, this effort has (so far) been unsuccessful."

The attorney general's office said in the briefs that a deal to obtain pentobarbital and vecuronium bromide from a pharmacy had fallen through. It did not identify the pharmacy.

If another drug is suitable to be used, Branham said, the state might change its protocols and still attempt to execute Clayton Lockett this Thursday. The other inmate, Charles Warner, is scheduled to die March 27.

Under Oklahoma law, two alternative means of execution are available, but only if lethal injection is deemed unconstitutional: electrocution and firing squad. Since this delay is based only on a drug shortage, the state cannot switch methods of execution, Corrections Department spokesman Jerry Massie said.

"Lethal injection would have to be declared unconstitutional. Those (electric chair and firing squad) are listed but only if lethal injection is declared unconstitutional," Massie said.

Oklahoma uses a three-drug execution process: Pentobarbital is a sedative, vecuronium bromide is a muscle relaxant and a third drug stops the heart.

"It's stunning news to us that the state does not have the means to carry out a legal execution right now, and it gives us deep cause for concern that they are coupling that revelation with an insistence on shrouding the process in secrecy," said federal public defender Madeline Cohen, who previously defended Lockett and Warner.

Lockett, 38, and Warner, 46, have argued it is improper for Oklahoma to conduct its executions behind a "veil of secrecy" and have asked for a delay in their executions while they seek to learn more about the drugs that would be used to kill them.

They fear the drugs could be impure and perhaps cause them undue pain as they are put to death, in violation of a constitutional prohibition against cruel or unusual punishment, according to their lawsuit.

The state argued in its court filing Monday that, in previous decisions, inmates were not allowed to challenge their executions just because something may go wrong.

The "risk of accident cannot and need not be eliminated from the execution process in order to survive constitutional review," Branham wrote.

The inmates' lawsuit doesn't challenge their convictions or sentences, just the portion of Oklahoma law that prevents anyone from obtaining information about the state's execution procedures.

Within the past month, both condemned men were denied clemency by the Oklahoma Pardon and Parole Board.

Lockett was found guilty in the 1999 shooting death of a 19-year-old Perry woman who was among of a group of people kidnapped from a home and taken to a remote location. Prosecutors say Lockett was among three attackers who laughed as the woman was buried alive.

Warner is set to be executed for the 1997 rape and murder of his girlfriend's 11-month-old daughter.