Homeland Security Secretary Janet Napolitano said the agents were "shot in the line of duty." One agent was critically wounded and died from his injuries. The second agent was shot in the arm and leg and remains in stable condition.
"Let me be clear: Any act of violence against our ICE personnel . . . is an attack against all those who serve our nation and put their lives at risk for our safety," Napolitano said.
The Mexican Foreign Ministry expressed its condolences and vowed to seek the assailants.
Attacks against U.S. law enforcement in Mexico are rare. An undercover U.S. drug agent was killed in the line of duty in Mexico in 1985, when the Drug Enforcement Administration's Enrique "Kiki" Camarena was kidnapped and tortured by narcotics traffickers in Guadalajara.
Camarena's killing, with the apparent complicity of corrupt Mexican officials, created a major strain in U.S.-Mexico relations and prompted a DEA investigation. At one point, U.S. investigators seized Mexican suspects and whisked them back to the United States for trial despite protests from the Mexican government.
Until now, the aggressive American response to Camarena's murder has often been cited to explain why Mexican drug cartels have not targeted U.S. authorities operating in the country, knowing they would provoke the wrath of the U.S. government.
According to Mexican news accounts, police say the attack against the ICE agents took place in the state of San Luis Potosi, on Highway 57 near the town of Santa Maria Del Rio.
The reason for the attack and the assailants' identities were not immediately clear. More than 34,000 people have died in drug violence in the past four years as Mexico has waged a U.S.-backed fight against criminal organizations, which have grown rich and powerful on proceeds from drug sales to the United States.
In March, a U.S. citizen and employee of the U.S. Consulate in Ciudad Juarez was ambushed and slain as she and her husband, an El Paso sheriff's deputy, were returning home from a children's birthday party. The slaying of Lesley Enriquez and her husband, Arthur Redelfs, has not been solved. Mexican authorities brought a man to court who claimed he ordered the killings, but there has been no trial.