(CNN) -- Gunmen opened fire on federal police officers at Mexico City's international airport Monday, killing three, officials said.
Two of the officers died at the scene, while a third was transported to a hospital and died there.
The gunmen were suspected drug traffickers and opened fire as police closed in on them, the Public Security Ministry said in a statement.
It was not clear whether there had been any arrests.
The shooting took place at Benito Juarez International Airport, the country's busiest.
Last year, authorities there seized 198 pounds (90 kilograms) of cocaine, the ministry said. So far this year, they have seized 440 pounds (200 kilograms) of the drug.
More than 47,500 people have died in drug-related violence throughout Mexico since December 2006, when President Felipe Calderon announced plans to deploy troops in efforts to combat drug cartels.
The violence is worse outside the heavily policed capital, though crime still manages to creep in.
Murder rates in Mexico City are half the national rate of 18 per 100,000 residents and are lower than homicide rates in U.S. cities like New Orleans and Washington.