Nineteen firefighters died while battling a fierce forest fire in Arizona, U.S. media outlets said.
It was the worst such tragedy in 30 years in the United States.
The firefighters were members of an elite corps and became trapped by the forest fire that spread rapidly with the aid of strong winds in an area known as Yarnell Hill.
An official with the forestry department, Art Morrison, said that the firefighting team was working to create a firebreak.
"In normal circumstances, when you're digging fire line, you make sure you have a good escape route, and you have a safety zone set up. Evidently, their safety zone wasn't big enough, and the fire just overtook them," Morrison said in remarks quoted by CNN.
The fallen firefighters "were heroes - highly-skilled professionals who, like so many across our country do every day, selflessly put themselves in harm's way to protect the lives and property of fellow citizens they would never meet," U.S. President Barack Obama said.
"Michelle and I join all Americans in sending our thoughts and prayers to the families of these brave firefighters and all whose lives have been upended by this terrible tragedy," he said in a statement released by the White House.
The fire forced the evacuation of residents of Yarnell, located about 130 kilometers (81 miles) northwest of Phoenix.
At least 200 of the 500 homes in that town have been damaged by the fire, which has destroyed some 800 hectares (2,000 acres) of woodlands, according to the spokesman for the Arizona state forestry department, Mike Reichling, as cited by the online edition of The Arizona Republic.
The fire coincides with the intense heat wave that on the weekend baked California, Nevada and Arizona, taking the thermometer above 45 C (113 F) and causing hundreds of people to be hospitalized.
The U.S. National Weather Service does not foresee any reduction in temperatures in the region until Tuesday. EFE