Two federal police officers suspected of working for drug traffickers opened fire on fellow officers in a crowded food court at Mexico City's international airport on Monday, killing three policemen as panicked witnesses dove for cover.

The suspects were captured in airport surveillance video and have been fully identified but remain at large, the federal Public Safety Department said in a statement.

The officers killed were on an anti-narcotics mission and had gone to the airport to catch the two suspects in the act of drug trafficking, the statement said. Two officers died at the scene, and another died of his wounds at a local hospital. The department didn't offer any other details about the botched mission.

But it said the two officers are part of an alleged drug trafficking network that includes officials from several federal and local government agencies assigned to the airport.

"The Federal Police has identified the two officers who opened fire and several investigative units are now focused on capturing them," the department said.

The airport said in a press statement that the terminal and flights were operating normally following what it described as "a dispute in an open-access area." But the food court remained blocked to public access for hours after the shooting.

The shooting took place shortly before 9 a.m. (10 a.m. EDT; 1400 GMT) at the airport's newest terminal, close to where vehicles drop off passengers but well outside the internal security checkpoints where workers and passengers are screened.

Three shots rang out at first, said witness Israel Lopez, a 23-year-old Mexico City student who had gone to the airport to see off a friend. Lopez didn't see who those shots were directed at, but then the gunfire came closer.

"We were in the food court, and some policemen came in and started shooting at another policeman who was on the floor," Lopez said.

"We dove to the floor and covered ourselves with chairs."

Lopez said the shooters wore blue uniforms like those of federal police who provide security at the airport. He said the shooters then ran to the parking area "as if they were pursuing somebody," and he lost sight of them.

Robert Gray, an evangelical missionary from Hart, Michigan, but who has lived with his family in the city of Puebla for the past four years arrived at the airport after the shooting with his wife, two daughters and son to catch a flight back to the U.S. to visit family.

"It's surprising to see it happening at the airport. It's one of the safest places in the city," Gray said.

Officials have long said that Mexico City's airport is used by traffickers to move drugs, money and illegal migrants. But violence related to drug trafficking has seldom, if ever, occurred in passenger areas at the airport itself.

The federal Public Safety Department said it had spent 18 months investigating corrupt federal and local officials who were part of a cocaine trafficking ring and had seized 648 pounds (294 kilograms) of cocaine during that time at Mexico City's airport.

In 2007, gunmen fatally shot high-ranking intelligence official Jose Nemesio Lugo, who investigated drug and migrant smuggling, as he drove to work. Lugo once served as the director of airports, seaports and border crossings for the Public Safety Department.

Later that year, the severed heads of three employees of a customs brokerage firm were found near the airport and in the nearby state of Mexico. The decapitations were apparently retaliation for the seizure of a half-ton of Colombian cocaine at the airport, officials said at the time.

In 2008, federal police chief Edgar Millan was gunned down inside his Mexico City home, and one of the suspects in that killing had worked as an anti-drug officer at the Mexico City airport.

The suspect had a notebook with detailed information on drug trafficking at the airport, and officials said federal investigations into those operations may have been a key motive for Millan's killing.

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Associated Press writers Olga Rodriguez, E. Eduardo Castillo and Mark Stevenson in Mexico City contributed to this report.