It's one of Washington's most truculent adversaries. North Korea's nuclear tests and sharp rhetoric have raised concerns about the safety of South Korea and how the United States ought to respond. The North Koreans have even threatened to pull out of the armistice that ended the Korean War.

Yet North Korea's harsh treatment of its own citizens - up to 200,000 people are believed to live under brutal conditions in prison camps - is often overlooked. The United Nations Human Rights Council is now considering a formal inquiry into possible crimes against humanity.

Tightly controlled images of the country show only propaganda, military drills and a people seemingly in cult-like devotion to their leader, Kim Jong-un, the scion of the political dynasty that has ruled North Korea since its establishment in 1948.

As ABC News' digital reporter Joohee Cho reports from Seoul, his people place him on a pedestal and North Korean state television has shown citizens pledging to sacrifice their lives to protect their "eternal shining star."

But conditions under Kim have become harsher, according to journalist and author Blaine Harden in an interview with Christiane Amanpour.

"He seems to have tightened up the border, making it harder for people to leave the country," said Harden. "And there seems to be an expansion of the prison camps."

The existence of the camps has been verified by satellite images with increasingly precise detail. But virtually no images or video of the prisoners have emerged, explaining partly why little attention has been paid to them. Harden described the camps as places with no exit, where prisoners are worked to death.

Shin Dong-hyuk was one of those prisoners, born and raised in a North Korean camp. Harden wrote of his life in the book "Escape from Camp 14." To date, Shin remains the only person ever known to have escaped one of the camps.

"Children in the camps are quite literally bred by the guards, who choose their parents, and they are raised to be disposable slaves," said Harden.

The first rule that guards teach prisoners is that the penalty for trying to escape is to be shot. One can also be shot, Harden said, for knowing a fellow prisoner's escape plans and not reporting them.

"When he heard his mother and brother talk about escaping, he turned them in when he was 13," said Harden. "His brother was shot and his mother was hanged in front of him."

In his early 20s, Shin was working with a newcomer to the camp who gave him a reason to risk his life and escape.

"This man told him what was out there and also told him that if he escaped, he could eat such things as grilled meat," said Harden. "It was visions of grilled meat that motivated his escape."

At age 23, Shin escaped the camp by crawling through barbed wire. He is now living in Seoul, where he's become a human rights activist. Shin's story has helped in the push for a formal inquiry by the U.N. into human rights abuses.

"I don't think it's possible for outsiders to change the way they behave towards their own people," said Harden. "But I think it makes the entire world aware that North Korea is more than just the sum of its nuclear and missile arsenal. That it survives in many ways by terrorizing its own people."