A North Korean defector interrupted a United Nations human rights press conference in Seoul on Thursday to plead tearfully to be allowed to go back to her relatives in Pyongyang.
But they often struggle to make a living in the capitalist South and sometimes fail to adjust to their new lives.
Dressmaker Kim Ryon-Hui arrived seven years ago but has since has made several desperate attempts to return to her family -- including forging a passport, for which she was imprisoned, and falsely confessing to espionage in the hope she would be expelled.
"I'm a citizen of of the Democratic Republic of Korea," Kim told dozens of reporters at a briefing in Seoul by Tomas Ojea Quintana, the UN's Special Rapporteur on human rights in the North.
"I have been forcefully detained in the South for seven years," she added.
Kim accused Seoul of violating her human rights, saying it had prevented her from going back to her aging parents and daughter.
"A mother is someone who can't be apart from her daughter for even a moment, but seven years just hurts too much," she said, her voice trembling, adding she had attempted suicide.
Most North Korean defectors are issued a South Korean passport six months after arrival, but Kim still has not received one and said the South's intelligence services had told her she "might escape to the North".
South Koreans need government permission -- which is only granted in exceptional circumstances -- to go to the North, with which the country is technically still at war.
Pyongyang repeatedly cites Kim's case and has said it will not allow any more reunions of relatives divided by the Korean War until she -- and 12 North Korean waitresses who it says were kidnapped from a restaurant in China -- are returned.
The divided families are one of the most emotive outcomes of the conflict, which saw the peninsula partitioned in 1953, with around 60,000 increasingly elderly South Koreans still hoping to meet their relatives again.
Quintana said the case was an example of the "absurd cost of division".
The North is accused by the UN and many other countries of widespread human rights violations and Quintana said social and economic structures that fulfil ordinary people's rights and needs had largely "disappeared".
"What remains intact is the comprehensive system of control and surveillance over the population," he said.
There was also a "widening gap in living standards between Pyongyang residents and the majority of the population".
"It is alarming that this situation occurs in a country that is devoting a vast proportion of its resources to its defence budget and strengthening its border controls in unprecedented ways," he added.
"The order of priorities in the DPRK requires a major shift that recognises the urgency to fulfil the basic needs of the population.