Two noncommissioned officers in the special forces have died of apparent suffocation and another has been injured during harsh training, military officers said Wednesday.

The accident took place late Tuesday in a unit of the Special Warfare Command in the central town of Jeungpyeong, some 126 kilometers south of Seoul, when the staff sergeants, identified only by their family names, Lee and Cho, collapsed during a training exercise meant to help them survive captivity situations, according to the officers.

They had spent more than an hour on their knees with their hands tied behind their backs wearing hoods over their faces during the training that was to let them experience the hardships they could suffer while being held captive.

A hospital official said suffocation may be to blame for the deaths, though the exact cause has yet to be determined. He spoke on condition of anonymity, citing policy.

The injured officer has received treatment, and has been recovering, according to the military officers.

"We are looking into exactly what happened to them by analyzing evidence, including footage from closed-circuit televisions and witnesses' accounts," an officer of the special forces unit said.

While the officer noted that no physical assaults or torture took place during the training, he admitted to the leadership's failure "to properly manage the intensive and dangerous training."

Taking a leaf from America's book, the South Korean military has introduced the captivity exercise for the first time this year, according to officers. (Yonhap)