The state of Texas executed Wednesday a Mexican man convicted of murdering a Houston police officer in 1994, despite a diplomatic outcry and pressure from the US federal government to further review his case.

Edgar Tamayo Arias, 46, who was denied an 11th-hour stay of execution by the US Supreme Court, was executed by lethal injection at 9:32 p.m. local time at a state prison in Huntsville, Texas, spokesman Jason Clark said.

The case of Arias had sparked widespread protests as he 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.

Mexico strongly denounced his execution as a violation of international law.

As Tamayo's last chance for a reprieve slipped away, anguished relatives gathered at his parents' home in Miacatlan in central Mexico, huddling next to radios listening for news from the United States and praying for a miracle.

"This pains us so much. We kept holding onto hope," said Karen Arias, one of Tamayo's nieces.

The inmate's lawyers had hoped to win a last-minute reprieve from the U.S. Supreme Court after failing to persuade lower courts, only to have their appeal for a stay of execution denied in a matter of hours.

His lawyers said he spoke very little English at the time of his arrest for the 1994 murder of Houston police officer Guy Gaddis, and is mentally handicapped.

"If he had had the assistance of the Mexican consulate at the time of trial, [Arias] would never have been sentenced to death," defense attorneys Sandra Babcock and Maurie Levin said in a statement.

In 2004, the UN's International Court of Justice ordered the US to provide judicial review of the convictions and sentences of Arias and 50 other Mexican nationals who were denied consular assistance.

'Violation of treaty commitments'

Arias was the third Mexican national to be executed in Texas without proper judicial review, and a fourth is scheduled to be executed in April.

"The execution of [Arias] violates the United States' treaty commitments, threatens the nation's foreign policy interests and undermines the safety of all Americans abroad," his lawyers added.

"It is now imperative that Congress promptly act to ensure passage of legislation that will bring the US into compliance with its international legal commitments and provide judicial review to the Mexican nationals who remain on death row in violation of their consular rights."

The 1963 Vienna Convention treaty, to which 176 nations are party including the U.S., sets out how authorities must act when foreign nationals are arrested or detained.

It involves notifying the individuals in question of their right to have their consulate informed of their arrest. They subsequently have the right to consular assistance.

"The damage to America's international reputation worsens with each execution, but the solution is simple -- just pass a federal law requiring a fair judicial review of these claims," said Mark Warren of Human Rights Research in an interview with AFP on Wednesday.

Mexico had asked repeatedly for Arias’s execution to be postponed.

U.S. Secretary of State John Kerry wrote to Texas Gov. Rick Perry late last year asking for a stay of execution until the consular assistance issue was reviewed.

The State Department has repeatedly emphasized the importance of the case on a wider diplomatic level, and warned that it could impact the consular access American nationals are able to receive when arrested abroad.

Tamayo became the fourth person put to death in the United States this year and the first in Texas.

Texas has executed 508 prisoners since the reinstatement of capital punishment by the U.S. Supreme Court in 1976, the most of any U.S. state.