Plans to introduce cyanide gas as a lethal alternative for death row prisoners in Arizona have been labelled "disgraceful" by Holocaust memorial groups.
The state's Department of Corrections purchased potassium cyanide and other ingredients to make the lethal gas last December, according to newly published records.
"For Auschwitz survivors, the world will finally come apart at the seams if in any place on this Earth the use of Zyklon B in the killing of human beings is considered again," Christoph Heubner, from the International Auschwitz Committee, said.
New documents reportedly show the department's invoices for a solid brick of potassium cyanide, sodium hydroxide pellets and sulphuric acid - the materials required to produce the gas.