A German manufacturer suspended shipments of a widely used drug to a US distributor this year after 20 vials were mistakenly sent to the state of Missouri to be used in executions.

Drug maker Fresenius Kabi said shipments of the anaesthetic propofol were halted to a Louisiana distributor for four-and-a-half months through mid-March.

It said it feared the European Union would ban exports of the drug altogether if it was used in executions.

"We felt it was important to make sure it was restricted to the healthcare professionals," said Geoffrey Fenton, a US spokesman for the firm.

Propofol, which is mostly made in Europe, is administered about 50 million times a year in the US during various surgical procedures, according to the manufacturer.

The Death Penalty Information Center said Missouri had been expected to become the first US state to use the drug in an execution scheduled for 23 October.

The death penalty is banned in the EU and it bans the export of drugs for use in executions.

Fresenius Kabi said it had stopped shipments to Louisiana distributor Morris & Dickson LLC from 1 November 2012 to mid-March 2013 after the US firm inadvertently sent a carton containing 20 vials to Missouri's department of corrections.

The German company confirmed it had suspended the shipments a day after Missouri announced that it would return the drugs to the distributor.

Missouri is taking the unusual step 11 months after the distributor frantically pleaded for the return of the vials, according to emails recently made public.

Richard Dieter, executive director of the Death Penalty Information Center, said he had never heard of a drug firm suspending shipments to a distributor over their possible use in US executions.

The move shows how US states and suppliers of drugs are coming under strong pressure from big pharmaceutical companies, especially in Europe, not to use supplies in executions.

The campaign against the death penalty has forced some states to change the drugs they use in lethal injections, find new supplies of existing drugs, or buy drugs from lightly regulated compounding pharmacies.