Thieves apparently targeting people who exchange money at Mexico City's international airport shot a French citizen in the head on Tuesday, and authorities warned that gangs have put lookouts at exchange windows in the terminal.

The 55 year-old French biotechnology researcher, who works at a Mexican university, was attacked and robbed of euro4,800 ($6,336) on a street near the airport, assistant city prosecutor Luis Vasquez and police said. He is in serious condition at a local hospital.

Officials at the French embassy said they could not confirm the victim's name or home town.

Mexico City police chief Manuel Mondragon said criminal gangs have posted lookouts at some of the money exchange businesses inside the airport. The lookouts tip off associates waiting outside who rob the victims after they leave the terminal. The gangs often use extreme violence.

The lookouts "send a message by radio or telephone about who has changed money ... and then cars are sent out to intercept the person," Mondragon said. "When the victim resists, it unleashes the most incredible violence, like shooting this man in the head."

The Frenchman's driver testified that two cars appeared to follow them after they left the airport, then cut them off, police said. One man got out with a gun and shot the victim when he refused to hand over the bag containing the money.

There have been about three other reported cases of foreigners being held up under similar circumstances in recent months, police say.

In one case, a tourist from Guinea was shot during a similar attack near the airport in January.

Vasquez said the two crimes may be related.

"We believe it could be members of the same gang, or another gang using the same methods," Vasquez said.

The airport itself is under the auspices of federal police, while the streets outside the terminal are patrolled by city cops.

Mexico has seen a wave of drug-related killings that claimed more than 5,300 lives in 2008, as well as violent kidnappings and common crime, but relatively few foreigners have been among the victims.

On Dec. 10, American anti-kidnapping expert Felix Batista was abducted in northern Mexico and has not been heard from since.