Opponents of the death penalty demonstrate outside Breard's jail in Jarratt, Virginia
Virginia governor James Gilmore went ahead with the execution of Angel Francisco Breard, 32, on Tuesday night despite opposition from the US State Department.
Breard, who was born in Argentina, had been sentenced to die by lethal injection for the murder and attempted rape in February 1992 of a 39-year-old neighbour, Ruth Dickie.
Breard confessed to the murder but said he was under a Satanic curse placed on him by his ex-wife's father.
He rejected a plea bargain which would have spared his life but pleaded for mercy from the jury.
Earlier this month Paraguay raised the case with the International Court of Justice which asked for a stay of execution.
Not afforded his rights
Paraguay's Deputy Foreign Minister Leila Rachid said: "It has been demonstrated that local laws, despite the international courts, can carry out the death penalty without any contemplation."
Virginia prosecutors admit Breard was not afforded his rights under the Vienna Convention on Consular Relations to meet with Paraguayan consular officials.
But they said it should have been raised with the state appeals courts that upheld the death sentence.
Ms Rachid said: "Neither Paraguay nor Argentina was notified of the imprisonment. A boy like that, with all his deficiencies and his linguistic limitations was subjected to the luck of the justice system of that country."
Radio channels in the Paraguayan capital Asuncion were inundated with angry callers.