The highest-level North Korean diplomat to defect to South Korea says he decided to flee last year because he didn't want his children to live "miserable" lives in the North.

Key points: Thae Yong-ho says his risky defection was for the sake of his sons

Thae Yong-ho says his risky defection was for the sake of his sons He expresses disappointment in North Korean leader Kim Jong Un

He expresses disappointment in North Korean leader Kim Jong Un The former deputy ambassador to the UK believes North Koreans will one day rise up

Thae Yong-ho, a former minister at the North Korean Embassy in London, told reporters in Seoul that he was lucky to have been able to bring both of his sons to London, unlike other North Korean diplomats who are forced to leave some of their children at home as "hostages."

After his sons, now 20 and 27, learned about life in Britain, they began asking him questions such as why North Korea barred use of the internet and executed people without proper legal procedures, he said.

Mr Thae said he decided to talk frankly with them about North Korea. He concluded that his sons would have "miserable" lives if they returned home because they had come to know the truth about the country.

"On the day when we got out of the embassy I told them that 'now I am going to cut the chain of slavery and you are the free men. You are not slaves anymore'."

He said his sons were happy and were "now feeling a true sense of freedom" in South Korea.

Mr Thae said his disappointment with North Korean leader Kim Jong Un was another reason he defected. He said he initially had some hopes for Mr Kim but eventually fell into "despair" after watching him execute officials without proper reasons and pursue development of nuclear weapons.

Mr Kim took office in late 2011 following his dictator father's death and has since orchestrated a series of high-profile executions, purges and dismissals in what outside analysts say is an attempt to bolster his grip on power.

His pursuit of nuclear weapons has drawn tough international sanctions.

Since his release into society last month following months of custody by South Korea's intelligence agency, Thae Yong-ho has conducted a series of media interviews in what he says is an attempt to reveal the truth about North Korea.

He said if North Koreans were able to obtain more information about their country's situation, it could trigger a public uprising against the Kim government.

North Korea has called him "human scum" and accused him of embezzling government money and committing other crimes.

AP