[Updated at 8:14 p.m.] One of two American immigration and customs officers who were shot in Mexico on Tuesday has died, the U.S. Department of Homeland Security said.
The two U.S. Immigration and Customs Enforcement special agents were shot while driving between Monterrey and Mexico City on Tuesday afternoon by unidentified gunmen, U.S. officials said.
"One agent was critically wounded in this attack and died from his injuries. The second agent was shot in the arm and leg and remains in stable condition," DHS Secretary Janet Napolitano said in a written statement.
The names of the agents weren't immediately released. It's not clear where the attackÂ happened on the 567-mile route between the two cities.
According to ICE, the agency has about 30 officers assigned to its office in Mexico City. They work a range of issues, including drugs, weapons, currency and immigration.
An ICE official, speaking on condition of anonymity, said these were the first shootings of ICE agents in Mexico.
U.S. law enforcement agencies are working with Mexican authorities "to ensure the perpetrators of this unconscionable crime are captured as quickly as possible," Napolitano said.
"Let me be clear: Any act of violence against our ICE personnel - or any DHS personnel - is an attack against all those who serve our nation and put their lives at risk for our safety," Napolitano said. "The full resources of our department are at the disposal of our Mexican partners in this investigation. We remain committed in our broader support for Mexico's efforts to combat violence within its borders.
The Mexican government "vigorously condemns this serious act of violence and expresses its solidarity with the United States government and the families of those attacked," Mexico's Ministry of Foreign Affairs said in a statement.
- CNN's Jeanne Meserve and Nick Valencia contributed to this report.FULL STORY