Obama, who spoke from Africa today, 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.
UPDATE- YARNELL, Ariz. (AP)- A wildfire that killed 19 firefighters in Arizona also destroyed an estimated 200 homes in a central Arizona community.
Dry grass near the communities of Yarnell and Glen Isla fed the fast-moving blaze, which was whipped up by wind and raced through the homes.
Nineteen firefighters died fighting the blaze.
Most people had evacuated from the town of 700, and no injuries or other deaths were reported.
The Red Cross has opened two shelters in the area -- at Yavapai College in Prescott and at the Wickenburg High School gym.
(CNN & NBC News) - Nineteen firefighters were killed Sunday battling a blaze in Arizona, the state forestry division said.
The vast majority were from Prescott, said Wade Ward with the Prescott Fire Department.
The crew was fighting the Yarnell Hill fire, which broke out Friday northwest of Phoenix.
A spokesman for the Arizona State Forestry Division said the firefighters were fighting the blaze near the town of Yarnell, Ariz., about 90 miles northwest of Phoenix. The fire, which was started by lightning, prompted evacuations of about 50 nearby homes. The Arizona Republic reported the state authorities plan to call in federal help to battle the 2,000-acre blaze.