Two pharmaceutical companies have joined a legal bid to prevent their drugs from being used to execute seven US prison inmates in the space of 11 days.
In a court filing, Fresenius Kabi USA and West-Ward Pharmaceuticals said they object to their products being used by the state of Arkansas for lethal injections as it "runs counter to the manufacturers' mission to save and enhance patients' lives".
They added that the use of their drugs "carries with it not only a public health risk, but also reputational, fiscal and legal risks".
The unprecedented schedule of executions was announced after Arkansas prison officials acquired a supply of potassium chloride, adding to the stock of midazolam they currently have.
The two drugs are part of the three used in lethal injection executions in the US.
Fresenius Kabi said it believes it manufactured the potassium chloride, while West-Ward is believed to have made the state's supply of midazolam.
However, both companies say they have put strict controls on supplies and do not know how their products were purchased by officials.
"We can only conclude Arkansas may have acquired this product from an unauthorised seller," a Fresenius Kabi spokesperson said.
"Pharmaceuticals obtained in this manner are at risk of adulteration or chemical change due to improper handling such as failure to maintain proper temperature levels during storage and transport."
London-based Hikma, West-Ward's parent company, said it made "repeated" representation to officials "to confirm if they are in possession of our product which they intend to use in lethal injections, and if so to return it to us".
Arkansas has not executed an inmate since 2005 due to drug shortages and legal challenges.
Prison officials plan to hold two executions a night from Monday, followed by a final one on Thursday.
If the seven executions are carried out as scheduled it would mark the largest amount of inmates put to death by a US state in such a short period in modern history.
Amnesty International said the "conveyor belt of death" demonstrated "how out of step Arkansas is with the rest of the world when it comes to state-sanctioned killing".
The legal challenge against the execution schedule, launched by the seven death row inmates, is expected to be adjudged on Friday.
Ahead of the decision protesters demonstrated outside the home of Governor Asa Hutchinson, who sanctioned the executions.
On Thursday, Mr Hutchinson defended the schedule, saying there was "insufficient attention that is paid to the victims and the families in these cases".
He added that he believed prison officials were able to source their new supply of drugs thanks to a 2015 state law that keeps the source of Arkansas' three lethal injection ingredients secret.
He said: "I don't think we would have acquired the drugs that we have without that confidentiality agreement."