Texas, the US state that puts to death the most inmates, has resolved a shortfall of a lethal execution drug, according to authorities.

Last month, an official said that the state's stock of pentobarbital had nearly run out and would only last through September.

Pentobarbital was used in an execution late Thursday "and it was not expired," Texas Department of Criminal Justice spokesman Jason Clark said.

It was unclear whether that dose was part of an old or new supply of the anaesthetic used to euthanise animals.

Mr Clark declined to provide any specifics but suggested the problem of replenishing the state's stock of the killer drug had been resolved.

"We have not changed our execution protocol in which pentobarbital is used and have no immediate plans to do so," Mr Clark said.

"We will continue to use pentobarbital in the future."

In August, authorities said the state would have to find an alternative - either another provider for the pentobarbital - or options that would involve other drugs.

US states that use capital punishment faced a supply problem in 2011 when the United States stopped producing the drug used since the introduction of lethal injections in the 1980s.

Since then, certain states - including Texas, which has executed more than 500 inmates in three decades - turned to pentobarbital.

But the Danish producer of the drug refused to provide it to the US for the purpose of executing humans.

Some US states, such as Ohio, plan to change methods or suspend executions while the matter is resolved.

Arturo Diaz, 37, was declared dead 17 minutes after receiving the pentobarbital injection last Thursday, according to prison authorities.

He had been sentenced to death for the April 1999 knifing murder near the Mexican border of a man who owed him $100.

His was the 27th execution in the US this year. Thirteen of these took place in Texas.

AFP