ANCHORAGE, Alaska (AP) - The asphyxiation death of a dog dropped from the Iditarod Trail Sled Dog Race has outraged animal rights activists who have long criticised the 1,600-km race as cruel.

People for the Ethical Treatment of Animals (PETA) is urging Alaska prosecutors to file cruelty charges against those responsible for the death of 5-year-old Dorado, who died last week after being buried by drifting snow at a checkpoint during severe wind.

"It's a horrifying death, and we feel it was totally preventable," PETA cruelty caseworker Kristin Simon said on Tuesday.

It was the first Iditarod dog death since 2009 when six dogs died, Iditarod chief veterinarian Stuart Nelson said.

The dog was found dead on Friday morning 418 km from the finish line. Dorado and other dropped dogs were last checked about 3am local time that day. The death was discovered as long as five hours later, according to race spokesman Erin McLarnon.

Dorado belonged to the team of Iditarod rookie Paige Drobny. The dog was dropped from the race on March 11 and was being held in a lot set up to care for dogs left behind because of illness, injury, or tiredness.

Dorado was removed from the race because he was moving stiffly, according to a blog posted on the website for the Squid Acres Kennel run by Ms Drobny and her husband. Iditarod officials have said Dorado was otherwise healthy.

Ms Drobny's husband Cody Strathe said they have asked race organisers to implement new protocols on how dropped dogs are cared for. He said changes sought from the Iditarod Trail Committee include boosting the number of helpers at checkpoints to check on dogs more often, providing adequate shelter and increasing the number of flights to get the dogs out more quickly.

"We thought that our dog was being cared for," he said. "That's the race organisation's responsibility. We, as mushers, trusted them."

Race officials have said the weather delayed efforts to transport dropped dogs sooner.

There were at least 135 dogs in the lot that night, and a race official told the Anchorage Daily News that locals, volunteers and veterinarians worked on protecting the animals from blowing snow and wind.

Most of the dogs stayed the night inside two airport buildings, while Dorado was among three dozen dogs held in a spot behind the buildings that handlers reportedly believed would protect them from the wind.

Nome District Attorney John Earthman said no decision has been made on whether to pursue charges.

"I believe I recognise their issue, which I believe is that somebody committed criminal negligence by leaving this dog out in the winter weather in western Alaska," he said.

"Whether someone can be successfully prosecuted for that, you know, I couldn't tell you. That remains to be seen."

Every year, the Iditarod is criticised by animal advocates as being an event that can be deadly for dogs and that the animals are forced to run. PETA says at least 142 dogs have died since the race began in 1973.

Mushers and race supporters say the race celebrates world-class canine athletes that have been conditioned through diet and training to perform at the highest levels of health after decades of research and advancements in animal care.