LINCOLN, Neb. (AP) — The American Civil Liberties Union of Nebraska says state prison officials may have misled authorities by indicating that four execution drugs obtained by the state were intended for medical purposes.

The organization sent a letter Monday to the Federal Drug Enforcement Agency, saying the state Department of Corrections and the State Penitentiary appear to have violated federal controlled substances laws by using its DEA registration to obtain the drugs, including fentanyl and potassium chloride.

The ACLU said the registration allows nurses to use controlled substances to help patients but doesn’t authorize the drugs for lethal injections. The organization, which also alleges the state may have illegally purchased fentanyl overseas, asked the DEA to investigate.

“Prisoners who are to be executed by lethal injection are not being diagnosed or treated, nor are they being provided any other form of medical care,” said Amy Miller, legal director of ACLU of Nebraska.

Dawn-Renee Smith, spokeswoman for the Department of Corrections, said the department legally purchased all of the drugs in the U.S.

“The ACLU is fabricating charges in a desperate attempt to foil the will of the people of Nebraska,” Gov. Pete Ricketts added.

The letter is the ACLU’s latest effort to halt Nebraska’s attempts to revive the death penalty. More than 60 percent of voters overturned the Legislature’s 2015 repeal of the death penalty, and the ACLU’s lawsuit over the voter referendum that reinstated capital punishment was recently dismissed.

Authorities acquired the drugs last year for the planned executions of death row inmates Jose Sandoval and Carey Dean Moore, though no dates have been set for the executions. The state’s last execution was in 1997.

Miller said that if the DEA agrees to investigate and finds violations, the Department of Correction’s drug licenses should be revoked and the lethal substances confiscated.