MEXICO CITY – More than 800 federal and local police have been assigned to improve security in and around Mexico City’s international airport after a series of armed robberies against travelers who exchanged money there, authorities announced Monday.

Mexico City Attorney General Miguel Mancera said 460 additional city police officers have been assigned to patrol the areas surrounding the airport. Federal police have added 350 new agents to the airport since December, said Federal Police Commissioner Rodrigo Esparza.

At least 18 people have been robbed recently outside the airport. They apparently were followed after doing business at the currency exchanges inside, according to city prosecutors.

Five of the victims were foreigners, including a French scientist who was shot and killed in January after assailants intercepted his car and stole 4,800 euros ($6,336).

The government also deployed 700 extra federal police Monday to Ciudad Juarez, a city bordering Texas where local police have been overwhelmed by drug violence. The police joined 3,200 federal troops who arrived in the city over the weekend.

Meanwhile in the western state of Michoacan, attackers threw grenades at a city police chief’s house and a police station on Monday in the city of Uruapan, injuring four officers, a state prosecutor said. Uruapan is one of many cities struggling with increasing drug violence. There were two other grenade attacks against police stations there in February.