The top United Nations human rights official said Friday that the execution of a Mexican national in Texas was a breach of international law, while diplomats, including Secretary of State Hillary Rodham Clinton, expressed disappointment in the outcome of the case.

Humberto Leal Garcia Jr., who had been convicted of raping and killing a 16-year-old San Antonio girl in 1994, was executed by lethal injection on Thursday night, shortly after the Supreme Court denied the Obama administration’s request for a delay.

The administration had filed an amicus brief in the case because of concerns that Texas authorities, in failing to notify Leal of his right to access Mexican consular officials, had violated the United Nations’ Vienna Convention.

In 2004, the International Court of Justice at The Hague ruled that Leal and other Mexican nationals facing execution had been denied their rights under the treaty.

The “execution will undermine the role of the International Court of Justice, and its ramifications are likely to spread far beyond Texas,” Navi Pillay, the U.N. high commissioner for human rights, said Friday.

U.S. officials had expressed concern about the impact of the case, suggesting that Leal’s execution could make other nations less likely to respect the terms of the Vienna Convention should American citizens abroad be in need of consular assistance.

Shortly after the execution, Mexico issued a statement of condemnation and said it had submitted an official protest to the State Department. A group of former U.S. ambassadors who had pressed for a stay also expressed disappointment.

“Texas justice is Texas justice,” said State Department spokesman Victoria Nuland. But, she added, “This is simply about ensuring an American — a non-American facing judicial proceedings in the United States — has the same rights that we expect an American facing judicial proceedings overseas would have.”

In seeking the stay, the Obama administration had sought more time so that Congress could take up pending legislation to bring the United States into compliance with the Vienna Convention.

The Supreme Court, however, ruled 5 to 4 that that was not enough to rule in the government’s favor, saying in an unsigned majority opinion that the court was tasked with ruling on current law, “not what it might eventually be.”

The immediate impact of the execution is unclear, and some experts have argued there is unlikely to be any.

They note that three years ago, Texas executed another Mexican national, even though he had similarly not been informed of his rights under the Vienna Convention. Then, too, there were warnings about the impact on U.S. foreign-policy interests.

“Congress,” the high court’s majority wrote Thursday, “evidently did not find these consequences sufficiently grave to prompt its enactment of implementing legislation, and we will follow the law as written by Congress.”