President Barack Obama is expressing condolences to families of North Carolina Air National Guard crew members who died in a crash fighting fires in South Dakota.

Obama said in a statement Monday the incident was still under investigation and offered no details about the circumstances of the crash.

He voiced concern for the well-being of survivors.

The military cargo plane crashed Sunday while fighting a wildfire in the Black Hills of South Dakota. The plane had six crew members aboard. Authorities said it crashed after dropping fire retardant.

The crash occurred two days after Obama visited the scene of wildfire damage in Colorado.

In his statement Monday, Obama praised those battling fires across the West, saying they were putting their lives on the line every day for their fellow Americans.