A US federal judge in Texas on Tuesday rejected a request for a stay of execution for a Mexican man convicted of murder, despite protests from both the US and Mexican governments.
Edgar Tamayo Arias, 46, is scheduled to be put to death by lethal injection on Wednesday for the 1994 murder of a policeman in Houston.
His case has sparked widespread protests, as Tamayo was not advised of his right to receive consular assistance at the time of his arrest -- in violation of the Vienna Convention on Consular Relations.
The 1963 treaty, to which 176 nations are party including the United States, sets out how authorities must act when foreign nationals are arrested or detained.
This involves notifying the individuals in question of their right to have their consulate informed of their arrest. They subsequently also have the right to consular assistance.
Federal judge Lee Yeakel rejected a request by Tamayo's lawyers for a stay as well as a review of the case, which the International Court of Justice has been demanding since 2004.
Yeakel ruled that the Texas Board of Pardons and Paroles had "provided Tamayo adequate due process" in accord with Supreme Court and federal court precedent.
His lawyers immediately said they would appeal, meaning the case could end up in the hands of the Supreme Court before the scheduled time of execution at 2300 GMT Wednesday.
The attorneys, Maurie Levin and Sandra Babcock, called the actions of the Texas Board of Pardons and Paroles "inexcusable," citing the "international repercussions" of the case.
"It is widely known that the Texas clemency process is the weakest in the nation, in the state that executes the most," they said, adding that the board had refused to consider evidence that Tamayo is mentally handicapped and that his trial was "fundamentally unfair."
Earlier Tuesday, the US government put pressure on Texas to grant a postponement.
State Department deputy spokeswoman Marie Harf said Washington was asking for "a delay in execution, until we can see whether denying him this access -- the consular access he's afforded under the Vienna Convention -- prejudiced the outcome."
"We've made our position very clear that this is an issue that could impact the consular access we get to American citizens overseas who are arrested," Harf added.
Secretary of State John Kerry wrote to Texas governor Rick Perry late last year, asking for a stay and emphasizing the importance of the case on a wider diplomatic level.
Mexico has complained bitterly about the imminent execution, and repeatedly asked for it to be postponed.
In central Mexico on Tuesday, about 200 people protested the scheduled execution in the city of Cuernavaca.
Demonstrators, many dressed in white, carried signs reading "What do we want for Edgar Tamayo? We want freedom!" and "We demand a pardon for Edgar Tamayo" as they marched towards the city's main square.