BOGOTA, Colombia (AP) — At least 13 people were injured following an explosion at a police station near Colombia’s border with Venezuela, officials in the city of Cucuta said on Monday.

Police said the explosion was caused by an “improvised explosive device” that was left at the station, which is located in one of Cucuta’s lower income neighborhoods.

So far authorities have refrained from blaming any of the armed groups that operate in the area. In June, a car bomb at a military base in Cucuta injured 44 people, including several U.S. soldiers who were there to train Colombian military personnel. Ten days later, President Ivan Duque’s helicopter was shot at as it approached the city’s airport.

Cucuta is the capital of North Santander province, which straddles the border with Venezuela and is also one of Colombia’s leading cocaine production areas. Several armed groups have been fighting over drug trafficking routes and coca fields in North Santander recently, including the National Liberation Army, a leftist rebel group, as well as a group led by former members of the FARC, the guerrilla group that made peace with Colombia’s government in 2016.

The Associated Press