Flickr/Matt Paish LONDON (Thomson Reuters Foundation) - A young North Korean defector who was trafficked and raped at the age of 13 after fleeing to China said on Friday that she hoped going public with her life story would shine a light on "the darkest place on earth", her homeland.

Yeonmi Park, 22, broke down in tears as she described seeing her mother raped when they fell into the hands of traffickers after crossing the frozen Yalu river into China in 2007.

Some 25,000 North Koreans have fled to South Korea in the last 20 years to escape famine and repression in the world's most secret state with many others living underground in China.

"The first thing I saw was my mum raped. This man was trying to rape me. I didn't even know what sex or kissing was, and my mother protected me," Park told the Women in the World summit in London during a tour to promote her newly released memoir "In Order To Live: A North Korean Girl's Journey to Freedom".

"They said if you are in China you have to be sold, you have to get married. And something that still saddens me is that I actually didn't care, I was so hungry.

"My mum was sold for $65 and I was sold for $260 - at the age of 13," said Park, now a rights advocate based in South Korea who campaigns against trafficking.

In her memoir, Park tells how she was sold, kidnapped and resold, ending up with a trafficker who made her an offer.

If she became his mistress he would buy her mother who had been sold to a farmer but if she refused he would hand her to the police who would deport her to North Korea where defectors are sent to labor camps or even executed.

"For a long time I thought of it as a business transaction, not rape," she writes. "Only now can I accept what happened in all its terrible dimensions."

Her captor not only raped her but soon forced her to help him traffic other North Korean women, including her own mother.

This Sept. 2, 2014 photo shows a new bridge connecting North Korea and China, seen from the North Korean side of the Yalu River border, where it touches down in rice fields in Sinuiju, North Korea. AP

"It was as if the blood had dried in my veins and I'd become another person. I didn't have pity for anyone, including the girls I helped sell, including myself," she writes.

Park describes a hierarchy of gangsters who specialize in the trafficking of North Korean brides in China, which has a shortage of women as a result of its one child policy.

"The ring of human traffickers always used the women before they were sold," she says.

Park said sometimes women asked to be sold into prostitution so they could make money to send home. She was told about brothels in Shanghai and Beijing where North Korean girls were injected with drugs so they couldn't run away.

After nearly two years with their captors, Park and her mother risked their lives to escape to Mongolia by crossing the frozen Gobi Desert using the stars to navigate.

Some critics have questioned her story but Park has apologized for any discrepancies, saying that at first she had not wanted to tell her full story but she was now determined that her book would be totally accurate.

In her memoir, Park urges China to end its policy of repatriating North Koreans as it fuels trafficking and slavery.

"I wish it had all never happened, and I never had to talk about it again. But I want everyone to know the shocking truth about human trafficking," writes Park, whose speech at the One Young World Summit in Dublin last year has received over 2 million views on YouTube.

"If the Chinese government would end its heartless policy of sending refugees back to North Korea, then the brokers would lose all their power to exploit and enslave these women."

(Editing by Belinda Goldsmith; Please credit the Thomson Reuters Foundation, the charitable arm of Thomson Reuters, that covers humanitarian news, women's rights, trafficking, corruption and climate change. Visit www.trust.org)