Colombian police are investigating two explosions that occurred on Tuesday in the border city of Cucuta that killed two policemen near the city’s airport. Though the explosions took place near the airport’s runway, the passenger terminal was not affected. But flights were suspended and passengers were evacuated from the building.

Defense Minister Diego Molano said the blasts were caused by “terrorist” groups that operate in the city of half a million people, which is located on the border with Venezuela and is a hub for commerce and migration.

Police said the first blast took place at 5 a.m. as a man carrying explosives tried to climb over a fence that separates the airport’s runway from one of the city’s neighborhoods. The man died instantly in the blast. About an hour later a second blast occurred as police inspected a package that had been left in the area, killing two members of the police’s anti-explosives squad.

Cucuta is the capital of North Santander state, a border region that has recently seen a surge in fighting between guerrilla groups and drug trafficking gangs that are vying for control of coca crops and trafficking routes. In June, a car bomb was set off at a military base in the outskirts of the city, where US military advisers were working. Then in August a bomb was set off outside a police station, injuring 14 people. President Ivan Duque’s helicopter was also shot at during a recent visit to the city. The president emerged unharmed from the attack.

Armed organizations operating in North Santander include the National Liberation Army guerrilla group, and dissident groups formed by former members of the Revolutionary Armed Forces of Colombia who refused to sign a 2016 peace deal with Colombia’s government.