(CNN) -- Federal police officers under investigation for drug trafficking opened fire on fellow officers at Mexico City's international airport, killing three, officials said.

Two of the officers died at the scene Monday, while a third was transported to a hospital and died there.

The officers who were shot were on their way to arrest the two gunmen after an investigation showed they had ties to a drug trafficking cell, the Public Security Ministry said in a statement.

"The two officers under investigation opened fire to avoid arrest when they spotted the federal police's investigation unit," the ministry said.

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.

CNNMexico.com contributed to this report