More elite teams are being sent to battle an out-of-control inferno that killed 19 firefighters Sunday in the southwestern U.S. state of Arizona.
A sudden wind storm turned the forest fire into one requiring the so-called "hot shot" crew that is trained to fight the fiercest fires. The flames swept over the victims late Sunday as they took cover in foil-lined emergency shelters.
It was the nation's biggest loss of firefighters in a wildfire in 80 years, and the deadliest single day for U.S. firefighters since September 11, 2001.
Officials say the number of firefighters is expected to more than double from the 200 on the scene early Monday.
U.S. President Barack Obama, who is in Africa, issued a statement early Monday calling the firefighters "heroes," and saying his thoughts and prayers were with the firefighters' families during the tragedy.
Arizona Governor Jan Brewer called it "as dark a day as I can remember." She added it may be days or longer before an investigation reveals how the tragedy occurred.
The fast-moving fire near the small town of Yarnell, about 130 kilometers northwest of Phoenix, has burned 34 square kilometers since Friday and destroyed several buildings.
Arizona, and the neighboring western states of California and Nevada are in the middle of an extreme heat wave. Temperatures have reached record highs, and excessive heat warnings are in effect across the region.