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By Jude Sheerin
BBC News, Washington
Native American tribal leaders in South Dakota are appealing for urgent help as snowed-in communities run out of vital supplies in the winter storm.
The Pine Ridge Indian Reservation has been buried in more than 30in (76cm) of snow, but powerful winds have stacked snow drifts 12ft (3.6m) high.
"We're fighting a losing battle," Oglala Sioux Tribe President Frank Star Comes Out told BBC News.
South Dakota's governor said she was deploying the National Guard.
Anna Halverson, who represents the Pass Creek District on the reservation, told the Darsha Dodge Rapid City Journal: "We're in a really extreme emergency down here.
"We have drifts as high as some houses that stretch 60, 70 yards at a time."
"I've seen across the reservation some members were burning clothes in their wood stove because they couldn't get access to wood," she added.
She said one family had run out of infant formula and other supplies and spent four days trapped inside their home, before walking eight miles to get help because their baby was starving.
Ms Halverson told the BBC the reservation is desperate, and would welcome help from any volunteers in the area.
"If anyone can come - we need anything and everything," she said.
The Oglala Sioux Tribe president told the BBC his community was cut off by impassable roads and were nrunning out of food, fuel and medicine.
"The [supply] trucks can't get out to a lot of residents because of snow drifts," said Frank Star Comes Out. "Sometimes when they do, they get stuck. And they have to be pulled out
"When we clear a road, the next day it just fills back in with blizzard conditions and blowing snow."
He said machinery is failing as diesel fuel turns to gel in the freezing cold. Some rescuers have been using horses and sleds, or just walking.
He said it was unclear how many of the tribe's 46,000 members were stranded across the reservation's three million acres, an area roughly the size of the state of Connecticut.
South Dakota Governor Kristi Noem has mobilised the state's National Guard to haul firewood from a nearby national forest to the Oglala Sioux Tribe and the Rosebud Sioux Tribe.
The troops will also help dig out tribal members trapped in the snow, which began dumping on the region a fortnight ago.
Wayne Boyd, chief of staff to the Rosebud Sioux president, told the Associated Press news agency: "We have families that are way out there that we haven't heard from in two weeks."