The US state of Texas is set to execute a Mexican national on Wednesday as appeals are rushed forward on possible trial irregularities or mental disability.
Ramiro Hernandez, 45, was sentenced to die in 2000 for allegedly murdering a 49-year-old man who employed him on his ranch in San Antonio. He also allegedly repeatedly raped his victim's wife following the murder.
Last week, the United States Supreme Court declined to hear an appeal from him as one of several Mexicans in US prisons seeking to challenge their sentences on the grounds they were not properly advised of their right to consular assistance after their arrest.
The Vienna Convention, ratified by 175 countries including the United States, dictates that foreign nationals must be able to receive consular assistance when arrested.
On Tuesday the Inter-American Human Rights Commission urged that the execution be suspended while authorities look into whether Hernandez was denied consular access.
Meanwhile, Amnesty International's Mexico office has appealed to Texas Governor Rick Perry saying that Hernandez is mentally disabled and therefore should not be executed.
While several of Herndandez's compatriots have been freed or seen their sentences commuted, three have been executed while around 40 remain on death row.
One of those executed -- Edgar Tamayo Arias -- was put to death in January despite appeals from US Secretary of State John Kerry and the Mexican government.
The Supreme Court did not give its reasons for turning down Hernandez's appeal, meaning he faces execution on April 9 at 6:00 pm (2300 GMT) in Huntsville, Texas.
Texas put to death a convicted serial killer last Thursday, after the US Supreme Court rejected his last-ditch appeal over the source of lethal injection drugs.
Tommy Sells was the 15th death row inmate to be put to death in the United States this year, and the fifth in Texas alone.
Last year, the Lone Star State accounted for more than a third of all US executions, according to the Death Penalty Information Center.
US states using the death penalty have faced crises over shortages of lethal injection drugs after European suppliers stopped supplying pentobarbital for use in human executions.
The shortage has prompted many US states to turn to unregulated compounding pharmacies to supply the drugs instead.
However, lawyers for many prisoners have said the compounded drugs can cause excruciating pain, putting executions using them in violation of the US Constitution, which forbids cruel and unusual punishment.
Texas authorities said the substances to be used in the executions had been tested and were found to be free of contaminants.