Three U.S. citizens detained in North Korea spoke to the U.S. television channel CNN on Monday with one pleading with the United States for help and another describing his situation as "urgent."

Kenneth Bae, who was arrested 18 months ago and sentenced to 15 years of hard labor for attempting to bring down the state, told CNN he was working eight hours a day, six days a week, and was the only inmate at a prison camp staffed by more than 20 officials, including a doctor.

"My health is failing," Bae said.