COLUMBUS, Ohio (AP) -- The sole U.S. manufacturer of a key lethal injection drug said Friday it is ending production because of death-penalty opposition overseas - a move that could delay executions across the United States.

Over the past several months, a growing shortage of the drug, sodium thiopental, has forced some states to put executions on hold. And the problem is likely to get worse with the announcement from Hospira Inc. of Lake Forest, Ill.

Hospira said it decided in recent months to switch manufacturing from its North Carolina plant to a more modern Hospira factory in Liscate, Italy. But Italian authorities demanded a guarantee the drug would not be used to put inmates to death - an assurance the company said it was not willing to give.

"We cannot take the risk that we will be held liable by the Italian authorities if the product is diverted for use in capital punishment," Hospira spokesman Dan Rosenberg said. "Exposing our employees or facilities to liability is not a risk we are prepared to take."

Italian Health Ministry officials were not immediately available for comment.

All but one of the 35 states that employ lethal injection use sodium thiopental. In nearly every case, they use it as part of a three-drug combination that sedates and paralyzes the inmate and stops the heart.

There are other, similar sedatives on the market, but substituting one drug for another would require new laws or lengthy administrative processes in some states, and could also lead to lawsuits from death row.

Similarly, switching to another manufacturer could invite lawsuits from inmates demanding proof that the drug will not cause pain in violation of their constitutional protection against cruel and unusual punishment. Hospira is the only sodium thiopental-maker approved by the Food and Drug Administration.

Because of what Hospira described as problems with its raw-material suppliers, sodium thiopental is already scarce in the U.S., and any batches Hospira made before it suspended manufacturing more than a year ago are set to expire this year.

In Texas, the nation's busiest executor, the Department of Criminal Justice said Friday it is exploring the use of another anesthetic. The state has four executions scheduled between now and July but has enough sodium thiopental to carry out only two February executions, spokesman Jason Clark said.

Ohio has enough to carry out a Feb. 17 execution but will not comment on its supply after that, or on Hospira's announcement, said Ohio prisons spokeswoman JoEllen Smith.

Hospira has long deplored the drug's use in executions but said it regretted having to stop production, because sodium thiopental has legitimate medical purposes as an anesthetic used in hospitals. Hospira continues to make two other drugs used in executions - pancuronium bromide, which paralyzes, and potassium chloride, which stop the heart.

Without providing details, Rosenberg said the company's state-of-the-art Italian factory was the only plant capable of manufacturing sodium thiopental.

Like most other European countries, however, Italy does not have capital punishment and opposes the death penalty. Italy's Radical Party brought a motion to Parliament, which passed overwhelmingly on Dec. 22, requiring Hospira to ensure that the drug would be used only for medical purposes and would not find its way into prisons.

The current shortage of the drug in the U.S. has delayed or disrupted executions in Arizona, California, Kentucky, Ohio and Oklahoma.

In the fall, states including Arizona, Arkansas, California and Tennessee turned to sodium thiopental made in Britain. But that supply dried up after the British government in November banned its export for use in executions.

Oklahoma went a different route, switching to pentobarbital, an anesthetic commonly used to put cats and dogs to sleep. The state has conducted two executions with that drug.