Mexican Foreign Secretary Marcelo Ebrard announced Sunday that Mexico would pursue legal action against the United States after three Mexican nationals were killed in the El Paso massacre on Saturday.
In a video posted to Twitter, Ebrard called the tragedy an "act of barbarism" over which Mexican President Andrés Manuel López Obrador has requested a forceful response.
"The president has instructed me to ensure that Mexico's indignation translates into ... efficient, prompt, expeditious and forceful legal actions for Mexico to take a role and demand that conditions are established that protect ... Mexicans in the United States," Ebrard said, according to NBC News.
"What has happened is unacceptable," he said.
In addition to the three Mexican deaths, nine Mexicans were injured in the attack, which U.S. officials have classified as domestic terrorism.
Ebrard said Mexican officials would explain further details about the legal steps they planned to take under international law at a press conference planned for later Sunday.
Martha Bárcena, Mexico's ambassador to the U.S., also condemned the attack Sunday.