The state of Missouri is threatening to resurrect the use of the gas chamber for executions, as an alternative to its dwindling supply of lethal-injection drugs.

The state's attorney general, Chris Koster, has warned that unless Missouri is allowed by the state supreme court to press ahead quickly with pending executions under its current lethal-injection protocol, its drug supplies will expire. In that case, the state might have to turn to the only other option open to it – the gas chamber.

"Unless the [supreme] court changes its current course, the legislature will soon be compelled to fund statutorily-authorised alternative methods of execution to carry out lawful judgments," Koster said. Under Missouri law only two forms of execution are permitted: "… by means of the administration of lethal gas or by means of the administration of lethal injection".

Koster's extraordinary statement, raising the possible return of the gas chamber, is a sign of the increasing fall-out on the 32 death-penalty states of the boycott on sales of medical drugs for use in executions. Drugs companies in America, Europe and Asia have refused on ethical grounds to sell their products to corrections departments, and the European Commission has imposed tough restrictions on the export of anaesthetics to the US.

As supplies became harder to procure, Missouri last year became the only state in the nation to turn to an execution protocol that used just one lethal injection, of the anaesthetic propofol in doses 15 times stronger than in usual surgical procedures. The new protocol was quickly challenged by 21 of the state's death row inmates, who argued the one-drug protocol was a violation of the US constitution, as it created "an unprecedented, substantial likelihood of foreseeable infliction of excruciating pain in the course of executing the plaintiffs".

In the wake of the legal challenge, the Missouri supreme court has refused to schedule any more execution dates until the question of the constitutionality of the new method of death is settled. That in turn has set the clock ticking on the state's limited supply of propofol.

Koster has filed new motions with the court this week, in which he pleads with the judges to be able to go ahead with the executions of two death row inmates, Joseph Paul Franklin and Allen Nicklasson, before the drugs expire. "The department has only three quantities of propofol remaining. The oldest quantity expires this October, the next batch expires in May 2014, and the newest supply expires in 2015. As each supply expires, the department's ability to carry out lawfully imposed capital sentences diminishes."

In the context of this logistical supply problem, Koster told the Kansas City Star that the gas chamber might be "the last option we have to enforce Missouri law".

Missouri switched from hanging as its preferred method of judicial killing to the gas chamber in 1937. The last time such an execution was carried out in the state was in 1965. In 1995, the US court of appeals for the ninth circuit in California ruled the gas chamber unconstitutional, under the prohibition of cruel and unusual punishment. Four years later a death row prisoner in Arizona skirted round the ban, by volunteering to die in that fashion.

Joseph Luby, an attorney with the Death Penalty Litigation Center in Kansas City who helped bring the legal challenge to the use of propofol in Missouri, said he would be surprised if the courts allowed the state to revive the gas chamber. "Its use has fallen into disrepute not least in the Western mind post World War Two. We see gas chambers as problematic for reasons that don't need spelling out."

Richard Dieter of the Death Penalty Information Center saw the Missouri attorney general's invocation of the gas chamber as a political ploy, directed at the state supreme court. "He's trying to prod the court into dropping its objections and setting execution dates by threatening that Missouri might have to go back to the dark ages if they don't act soon," he said.