U.S. Border Patrol agents recently uncovered and shut down a nearly 3,000-foot-long drug smuggling tunnel beneath the U.S.-Mexico border.

Discovered in early April while still under construction, the tunnel connected Tijuana, Mexico, to San Diego, California. According to U.S. Customs and Border Protection, the underground passage ran beneath the Otay Mesa Port of Entry and was intended to emerge near or within a commercial warehouse in San Diego.

Upon entering the “highly sophisticated” tunnel, authorities encountered barricades that appeared designed to conceal the entrance from law enforcement, according to the announcement. The tunnel stretched 2,918 feet in length and reached depths of approximately 50 feet. Measuring 42 inches high and 28 inches wide, it was outfitted with lighting, electrical wiring, ventilation systems, and a rail track system to move large quantities of contraband, Fox News reported.

Border Patrol agents, in coordination with Homeland Security Investigations and Mexican authorities, located the tunnel’s entrance on Monday inside a residence in the Nueva Tijuana neighborhood of Tijuana. According to the announcement, the entry point had been recently concealed beneath newly laid tile.

U.S. Customs and Border Protection stated that thousands of gallons of concrete will soon be poured into the tunnel to ensure it cannot be used by foreign terrorist organizations. “As we continue to strengthen the nation’s air and maritime border security, it’s not surprising that foreign terrorist organizations would resort to underground routes,” Jeffrey D. Stalnaker, acting chief patrol agent of the San Diego Sector, said in a statement.

“Disruption of narcotics smuggling tunnels is critical to protecting American lives,” he said, adding: “I’m grateful for the exceptional work of the Tunnel Team agents who placed themselves in danger, as well as the cooperation of our Mexican law enforcement partners.”

The report said that more than 95 tunnels had been located and decommissioned in the border sector since 1993, the announcement added.