Obama, who spoke from Africa on Monday, added that America's thoughts and prayers go out to their families.
He said, quote, "We are heartbroken about what happened."
Obama says his administration is prepared to help Arizona investigate how the deaths happened. He predicted the incident will force government leaders to answer broader questions about how they handle increasingly destructive and deadly wildfires.
The firefighters, members of an elite crew fighting a forest fire northwest of Phoenix, were overtaken Sunday by a fast-moving blazed fueled by hot winds. Some 200 homes also were destroyed.