Tercero is scheduled to be executed by lethal injection tomorrow for killing high school English teacher Robert Berger while robbing a Houston dry cleaning business in 1997.
The impending execution has sparked protests in Nicaragua, which abolished capital punishment in 1979, when the leftist Sandinista rebels came to power.
"For us here in Nicaragua, where we don't have the death penalty and embrace a spirit of humanitarianism and solidarity, it seems pathetic to be on the verge of a Nicaraguan citizen's execution," said the country's ambassador yesterday to the Organization of American States, Denis Moncada.
Activists have called a demonstration later in the day to demand Tercero be spared.
Nicaraguan national Bianca Jagger, a campaigner for the abolition of the death penalty, is one of those leading the protest movement.
"His execution would constitute an egregious miscarriage of justice," she wrote in an online petition signed by more than 500 people.
Jagger, the ex-wife of Rolling Stones singer Mick Jagger, said Tercero had "abysmal" legal representation and that his case was fraught with errors.
"I call with all my heart on the US authorities to accept the petitions to save Bernardo Tercero's life," said Cardinal Miguel Obando.
