Another tunnel has been discovered along the U.S.-Mexico border. That’s the fourth tunnel this week authorities have found.

The latest one was discovered Friday in Nogales, Ariz.. Federal investigators say the incomplete tunnel didn't appear to be in use. They believe it would have been used to smuggle drugs into the U.S. No arrests have been made so far.

On Wednesday authorities in Yuma County revealed a sophisticated drug-smuggling tunnel found after an earlier drug bust. The 250-yard-long tunnel was equipped with lighting and ventilation. The underground passageway started in Mexico and ended at an empty store in a strip mall in the border town of San Luis. Investigators say it may have been used to smuggle humans and weapons as well as drugs.

In Tijuana, Mexican authorities found two incomplete tunnels this week. One tunnel also had electricity and ventilation systems. The other one extended more than a thousand feet toward the U.S. border. Police found 50 tons of marijuana stashed at that location.