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Three people died and two were taken into custody Monday after the group got lost while crossing into the United States border near Mount Laguna in San Diego County, California, according to U.S. Customs and Border Protection.

Border Patrol dispatch was notified at around 2:15 p.m. local time Monday that five people needed medical help near La Posta Indian Reservation, a "very rural and extremely rugged" area by the Laguna Mountains, San Diego Sector Border Patrol said in a statement.

The rescue attempt came amid treacherous weather conditions. Early the same day, the National Weather Service office in San Diego tweeted that there was "heavy snow with poor visibility" on Mount Laguna.

Mt Laguna at 5 AM. Heavy snow with poor visibility.



Be prepared for chain restrictions. There are several already in effect in the San Bernardino Mtns, and should expand into SD County mountains through the day. #cawx pic.twitter.com/7bODdeXgF8 — NWS San Diego (@NWSSanDiego) February 10, 2020

Two of the five were able to walk out of the area on their own and told Border Patrol that three others needed to be rescued, San Diego Sector Border Patrol said. Within a few hours, the remaining three individuals were reached by helicopter; two were in grave condition and unresponsive, while the other was in serious condition.

Border Patrol agents provided immediate medical attention to the three on the scene. But just after 10 p.m., Chief Patrol Agent Aaron Heitke tweeted that all three had died.

"Due to severe weather, recovery of the bodies must wait until tomorrow," he wrote.

Between 4 and 5 inches of snow fell on Mount Laguna on Monday, the weather service reported. The group had called 911 when they started suffering from hypothermia, Heitke said on Twitter.