A sudden onset of triple-digit heat led to a rash of deaths among illegal immigrants during the weekend in Arizona's deserts, with 12 people reported dead between Friday and Monday.
Scores more were saved in nearly 50 rescue operations, U.S. Border Patrol spokesmen said.
The deaths were scattered along Arizona's border with Mexico, but most of the bodies were found west of Tucson.
Under a federal border control initiative, about 200 extra agents have been brought into the region for the summer months.
Heat-related deaths have become common in Arizona as immigrants have been pushed into remote and harsher terrain by agents cracking down in other border areas. The state is the busiest illegal entry point on the nation's southern border.
In the fiscal year ended Sept. 30, 55 immigrants died in Arizona because of the heat, according to the Border Patrol (search), out of a total of 172 illegal immigrant deaths in the state during that period.
Temperatures reached 110 degrees Sunday in Tacna, east of Yuma, which is at the California line. On Friday, the thermometer climbed to 106 in Sells on the sparsely populated Tohono O'odham Indian Reservation (search) southwest of Tucson.
Border Patrol agents in the agency's Yuma office conducted a dozen rescues over the weekend. Search-and-rescue supervisor Dan Sprick called it his team's busiest three-day period ever as they found 40 people stranded in the desert.
Another 37 rescues were conducted in the Tucson sector, which covers all but the westernmost part of Arizona's border with Mexico.
The immigrants repeatedly told Border Patrol agents that their smugglers, known as coyotes, had instructed them to "only grab a gallon or two of water. They never said anything about walking for two or three days," Tucson sector spokesman Luis Garza said.
"What scares me is that there just continues to be very widely scattered deaths," said the Rev. Robin Hoover, founder of Humane Borders (search), a Tucson-based organization that puts out jugs of water in areas of the desert used heavily by illegal immigrants.