Public executions and torture are daily occurrences in North Korea's prisons, according to dramatic testimony from former inmates at a U.N. Commission of Inquiry that opened in South Korea's capital on Tuesday.

This is the first time that the North's human rights record has been examined by an expert panel, although the North, now ruled by a third generation of the founding Kim family, denies that it abuses human rights. It refuses to recognise the commission and has denied access to investigators.

Harrowing accounts from defectors now living in South Korea related how guards chopped off a man's finger, forced inmates to eat frogs and a mother to kill her own baby.

"I had no idea at all ... I thought my whole hand was going to be cut off at the wrist, so I felt thankful and grateful that only my finger was cut off," said Shin Dong-hyuk, punished for dropping a sewing machine.

Born in a prison called Camp 14 and forced to watch the execution of his mother and brother whom he turned in for his own survival, Shin is North Korea's best-known defector and camp survivor. He said he believed the U.N. panel was the only way to improve human rights in the isolated and impoverished state.

"Because the North Korean people cannot stand up with guns like Libya and Syria ... I personally think this is the first and last hope left," Shin said. "There is a lot for them to cover up, even though they don't admit to anything."

There are a 150,000-200,000 people in North Korean prison camps, according to independent estimates, and defectors say many inmates are malnourished or worked to death.

After more than a year and a half ruling North Korea, Kim Jong Un, 30, has shown few signs of changing the rigid rule of his father, Kim Jong Il, and grandfather, state founder Kim Il Sung. Neither have there been signs of a thaw or loss of control inside the tightly controlled state.

Jee Heon-a, 34, told the Commission that from the first day of her incarceration in 1999, she discovered that salted frogs were one of the few things to eat.

"Everyone's eyes were sunken. They all looked like animals. Frogs were hung from the buttons of their clothes, put in a plastic bag and their skins peeled off," she said. "They ate salted frogs and so did I."

Speaking softly, she took a deep breath when describing in detail how a mother was forced to kill her own baby.

"It was the first time I had seen a newborn baby and I felt happy. But suddenly there were footsteps and a security guard came in and told the mother to turn the baby upside down into a bowl of water," she said.

"The mother begged the guard to spare her, but he kept beating her. So the mother, her hands shaking, put the baby face down in the water. The crying stopped and a bubble rose up as it died. A grandmother who had delivered the baby quietly took it out."

"TOUGH NUT"

Few experts expect the commission to have an immediate impact on the rights situation, although it will serve to publicise a campaign that has little visibility globally.

"The U.N. has tried various ways to pressure North Korea over the years in the field of human rights, and this is a way to raise the pressure a bit," said Bill Schabas, professor of international law at Middlesex University in Britain.

"But it's obvious that North Korea is a tough nut to crack and the U.N.'s means are limited. There would need to be profound political changes in North Korea to make headway in the field of human rights."

But there appeared to be little interest in the issue in Seoul. Only a few dozen people, including journalists, attended the public hearing at a city centre university.

Defectors are largely shunned or ignored in South Korea and eke out an existence in menial jobs, if they have them at all, according to official data.

Kim Jong Un stepped up the nuclear weapons and rocket programmes launched by his father with a third nuclear test and two rocket launches and emphasises the military in his speeches.

This year, he threatened the United States, South Korea and Japan with nuclear attack and although the country's bellicose moves were dismissed as empty rhetoric, Kim succeeded in driving tension on the divided Korean peninsula sharply higher.

The hope of many activists would be for the Kim dynasty to fall and for leaders in Pyongyang to be put on trial at the International Criminal Court (ICC) in The Hague, although the U.N. commission says this is not possible for the moment.

On its website, the Commission said it was "not appropriate" to comment on any ICC jurisdiction over potential crimes against humanity as North Korea had not signed the statutes that would enable the court to prosecute.

But activists said word of the commission would seep into the North via unofficial contacts maintained by families.

"People living their daily lives here don't realise how important this is. It will have a tremendously powerful impact across North Korea," said Kim Sang-hun, chairman of Database Center for North Korean Human Rights, a South Korean group.