US President Barack Obama said the 19 firefighters killed in the Arizona wildfire blaze were "heroes" who "selflessly put themselves in harm's way" to protect fellow citizens.
He said: "Yesterday, nineteen firefighters were killed in the line of duty while fighting a wildfire outside Yarnell, Arizona.
"They 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.
"In recent days, hundreds of firefighters have battled extremely dangerous blazes across Arizona and the Southwest. The federal government is already assisting, and we will remain in close contact with state and local officials to provide the support they need.
"But today, 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."