A secret tunnel discovered last week on the U.S.-Mexico border will be sealed by Mexican authorities, an army official in Ciudad Juarez said Saturday.

U.S. Border Patrol agents and Homeland Security Investigations uncovered a man-made tunnel entering the U.S. from Mexico on Thursday. Agents discovered it in El Paso, Texas, near a storm drain system by the border wall during a security sweep of the area.

Workers have begun using concrete to close a narco tunnel that officials believe was build within the past year. The tunnel investigation continues.