(CNN) -- The United States breached international law by executing a Mexican national without having granted him consular access, the U.N. High Commissioner for Human Rights said Friday. 

Navi Pillay, in a statement, said she deeply regrets the execution of Humberto Leal Garcia, after a 5-4 decision by the U.S. Supreme Court denied him a stay of execution Thursday night. 

"The execution of Mr. Leal Garcia places the U.S. in breach of international law," said Pillay, who is on an official mission in Mexico. "What the state of Texas has done in this case is imputable in law to the U.S. and engages the United States' international responsibility." 

Pillay said Leal was not granted consular access, which -- as a foreign national -- was his right under Article 36 of the Vienna Convention on Consular Relations. 

The denial of access raises concerns about whether Leal got a fair trial, Pillay said. 

Leal, who was convicted for the 1994 rape and murder of a 16-year-old girl, was executed Thursday evening by lethal injection in Texas. 

Federal officials, including the Obama administration, had tried to persuade Texas Gov. Rick Perry to delay the execution. "The secretary herself is quite disappointed in the outcome in this case," said State Department spokeswoman Victoria Neuland about Secretary of State Hillary Clinton. 

"The U.S. government sought a stay of Leal's execution in order to give the Congress time to act on the Consular Notification Compliance Act, which would have provided Leal the judicial review required by international law." 
What is Pillay doing in Mexico?
official mission