Mexican soldiers arrested nine people Tuesday after finding a suspected drug tunnel underneath a house in Tijuana.

The entrance to the tunnel was hidden inside a wardrobe in a house next to a Mexican Air Force installation and a regional federal police facility, Reuters reports.

The tunnel was wired with lights and extended north about 500 feet, but it was not believed to have entered American soil, according to Lauren Mack, a spokeswoman for the U.S. Immigration and Customs Enforcement.

Soldiers caught the suspects as they tried to flee the construction site and seized a truck allegedly being used to carry dirt away, the U-T San Diego reports.