Feds discover 'most sophisticated' cross-border tunnel with extensive ventilation, rail system

The partially completed passage was located last month

Immigration enforcement agents have uncovered a cross-border tunnel that U.S. Customs and Border Protection (CBP) is saying could be the "most sophisticated" yet.

Stretching from San Luis, Ariz. to San Luis, Mexico, the smuggling passageway includes a fully developed ventilation system, electrical wiring and a rail system. According to Immigration and Customs Enforcement (ICE), authorities discovered the tunnel in late July, before it could be completed.

A shovel sticks out of the sand as excavation work continues at the tunnel side (Courtesy of ICE via AP)

A shovel sticks out of the sand as excavation work continues at the tunnel side (Courtesy of ICE via AP)

Photos show the tunnel measured three feet wide and four feet high.

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The discovery was made during an ongoing, multi-agency effort by Homeland Security Investigations (HSI).

“This appears to be the most sophisticated tunnel in U.S. history, and certainly the most sophisticated I’ve seen in my career,” Border Patrol Yuma Sector's Acting Chief Patrol Agent Carl Landrum said in a statement Thursday. “We will continue to work closely with our partners – Homeland Security Investigations and state and local agencies -- to provide the best national security possible.”

This photo provided by U.S. Immigration and Customs Enforcement shows a section of an incomplete tunnel intended for smuggling, found stretching from Arizona to Mexico. (Courtesy of ICE via AP)

This photo provided by U.S. Immigration and Customs Enforcement shows a section of an incomplete tunnel intended for smuggling, found stretching from Arizona to Mexico. (Courtesy of ICE via AP)

In this undated photo provided by U.S. Immigration and Customs Enforcement, excavation work continues at a site of an incomplete tunnel intended for smuggling, found stretching from Arizona to Mexico. (Courtesy of ICE via AP)

In this undated photo provided by U.S. Immigration and Customs Enforcement, excavation work continues at a site of an incomplete tunnel intended for smuggling, found stretching from Arizona to Mexico. (Courtesy of ICE via AP)

Earlier this year, authorities announced they had found the longest known border smuggling tunnel, which stretched from Tijuana to San Diego. The tunnel originated near the Otay Mesa Port of Entry and measured 4,309 feet long -- more than three-quarters of a mile. The next-longest tunnel in the U.S., discovered in San Diego in 2014, was 2,966 feet long.

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In March, authorities located a tunnel containing a variety of drugs -- including about 1,300 pounds of cocaine, 17 pounds of heroin, and two pounds of fentanyl. CBP has warned in the past that drug trafficking from the U.S.-Mexico border region results in the loss of American lives.

News of the tunnel came on the same day that CBP Commissioner Mark Morgan held a press conference in which he warned about the scourge of smuggling.

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"As the U.S. continues to take on the challenges posed by COVID-19, we must secure our borders from illegal aliens who show their complete disregard of even the most basic application of health and safety precautions, which have become our new norm against COVID-19," said Morgan, showing pictures of container trucks packed with migrants

He added that criminal organizations and smugglers provide false promises to migrants and "have no concern for their safety or the safety of American citizens -- again in this backdrop of COVID-19." He explained that the migrants are kept in crowded, unsanitary stash houses for days in the sweltering heat, a situation he described as a "perfect incubator" for the new coronavirus.

The Associated Press and Fox News' Morgan Phillips ontributed to this report.