(Adds details on casualties, fleet grounding; statement by President Obama; byline)
By David Bailey
July 2 (Reuters) - An Air Force C-130 tanker has crashed while battling a South Dakota wildfire, killing and injuring crew members and forcing the grounding of a fleet of eight such firefighting planes, the U.S. military said on Monday.
The cause of the Sunday evening crash of the tanker from the North Carolina Air National Guard's 145th Airlift Wing has not been determined, and the U.S. Northern Command released few details about the crash.
"There were casualties, and our thoughts and prayers go out to those who were injured and those who lost their lives," the Northern Command said in a statement, without saying how many crew members were killed or injured.
The airplanes typically carry a crew of six when they are equipped to fight fires, and can drop 3,000 gallons (11,000 liters) of water or fire retardant in less than five seconds, enough to cover an area one-quarter mile long (0.4 km) and 100 yards (91 meters) wide. They can be refilled in 12 minutes.
President Barack Obama said that the crew, the families and their loved ones were "in our thoughts and prayers."
"The airmen who attack these fires from above repeatedly confront dangerous conditions in an effort to give firefighters on the ground a chance to contain these wildfires - to save homes, businesses, schools, and entire communities," the president said in a statement. "They are heroes who deserve the appreciation of a grateful nation."
The C-130 that crashed was one of eight the U.S. Air Force has that can be quickly converted into firefighting tankers under a Defense Department-U.S. Forest Service program when private and commercial fleets cannot meet the need.
The crash was at least the second of a tanker plane fighting U.S. wildfires this year after a privately owned Lockheed Martin P2V crashed while dropping flame retardant on a Utah blaze last month, killing both crew members on board.
But Sunday's crash was the first in the 40-year history of the joint Defense Department-Forest Service program, and the Northern Command said the remaining C-130s were on an operational hold on Monday.
"We all need to make sure our crews and planes will be ready to re-engage in the mission safely," Colonel Jerry Champlin, commander of the 153rd Air Expeditionary Group commander, said in a statement.
All eight of the tankers had been activated at the same time for the first time since 2008 to help fight numerous wildfires in Colorado and three other western states.
They were all based temporarily at Peterson Air Force Base in Colorado Springs, and the C-130 that crashed had been sent to support efforts to contain the White Draw Fire in South Dakota.
The most destructive wildfire in Colorado history burned 346 homes and forced 32,000 people from their homes in and around Colorado Springs last week.
South Dakota's White Draw Fire started on Friday afternoon and had consumed about 4,200 acres (1,700 hectares) as of Sunday, said Brian Scott, lead information officer for the incident team.
The fire is about five miles (eight km) north of Edgemont, South Dakota, which is not threatened, and was about 30 percent contained on Sunday, Scott said. (Reporting by David Bailey; Editing by Greg McCune, Cynthia Johnston and Eric Walsh)