( CNN ) -- Gunmen opened fire on two U.S. immigration agents in Mexico on Tuesday , killing one and injuring the other , officials said . The two agents with U.S. Immigration and Customs Enforcement ( ICE ) were attacked Tuesday afternoon while driving between Mexico City and Monterrey . One of the agents was gravely wounded and died later Tuesday . The other was in stable condition after being shot in the arm and leg , according to a statement released by the U.S. Department of Homeland Security . The shooting took place about 23 miles north of downtown Mexico City at approximately 3 p.m . ET , an ICE official said . The official spoke to CNN on the condition of anonymity because the case is still under investigation . The agents , according to the official , were doing `` routine work , '' traveling on a well-traveled highway in an armored car with diplomatic plates . They were forced off the road in Ojo de Aqua and surrounded by a group of more than 10 people . Prior to the shootings the agents apparently identified themselves as diplomats , the official said . The shooting provoked a swift condemnation from the U.S. government . DHS Secretary Janet 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 . `` The full resources of our department are at the disposal of our Mexican partners in this investigation , '' Napolitano said . `` I am deeply saddened by the news , '' Napolitano said . Senator Joseph Lieberman , I-Connecticut , who chairs the chamber 's Homeland Security and Governmental Affairs Committee , called the shootings `` the latest reminder of the grievous violence south of our border that must be stopped . '' One official said the victims , whose identities have not been released , were the first ICE agents to be gunned down in Mexico . 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 . `` ICE is working with the U.S. State Department , Mexican authorities and other U.S. law enforcement partners to investigate the shooting , '' the agency said in a statement . `` Our thoughts and prayers are with our colleagues . '' ICE Director John Morton said the `` tragedy is a stark reminder of the risks cofronted and the sacrifices made by our men and women every day . Mexican officials also released a statement on the shootings . `` Mexico 's government vigorously condemns this serious act of violence , and expresses its solidarity with the United States Government and the families of those attacked , '' the statement read . `` Federal authorities , in coordination with state cooperation , have an ongoing investigation to clarify what happened and bring to justice those responsible . '' CNN 's Jeanne Meserve and Mike Ahlers contributed to this report .
NEW : Mexican government confirms CIA agent slain in gun attack . Second victim in stable condition after being shot in the arm and leg . U.S. officials , Mexican government denies involvement .