North Korea's former deputy ambassador to the UK, who defected to South Korea in 2016, tells CNN he was like "a modern slave."

"I did not want to let my sons lead a life like me," Thae Yong-Ho told CNN's Christiane Amanpour on Thursday from Washington, where he was testifying before Congress.

Thae, as a senior diplomat, was exposed over many years to a grim juxtaposition: The draconian politburo that controls his country, and the freedoms of the countries in which he served.

That was only heightened in recent years, under the leadership of Kim Jong Un.

"He faced some challenges inside the leadership of North Korea," Thae explained. "That's why Kim Jong Un decided to show he is a man with mercilessness -- so that everyone should be frightened about him."

Thae said his sons had "a long dream of freedom," and wanted to continue their lives outside the yoke of Pyongyang. But "as sons," he said, they were unable to raise the idea of defecting with their father.

"When they heard my decision then they were very happy, and they really appreciated that I decided to let them free."

As a diplomat in London, Thae said, he tried to convey truths to Pyongyang -- to a point.

"I always report[ed] what was going on in UK and America and around the world," he told Amanpour. "But whenever I report[ed] those things, I always tried to keep a kind of line of loyalty to the system, and regime."

Family politics

CNN spoke to Thae's family in North Korea earlier this year, as part of a government-organized interview.

His sister, Tae Ok Ran, told CNN's Will Ripley that she wanted to "warn him" that "the whole family won't forgive him."

Thae's brother, Tae Yong Do, said Yong-Ho brought shame on the family, and that they see him as nothing more than a propaganda tool of the South.

"If I don't wash this sin away by myself, my sons and generations will have to work harder to pay for this," Tae Yong Do said at the time.

Despite their harsh remarks, Thae Yong-Ho said he was grateful that he was able to see video of his family.

"I was happy to watch the interviews," he told Amanpour. "So far I think they looked okay."

"It made me very happy, because I was able to see anyway their faces. And the place where the interview took place, I learned that it was actually the house of my sister. And I was very pleased to see their faces again, and I never imagined that I could see their faces in my life."

Mood for military action 'very high'

Thae warned Amanpour that "the mood for possibility of military action is very high" in North Korea and that it behooves all involved to "avoid any possible nuclear conflict."

He conceded that President Donald Trump's "fury and fire" rhetoric earlier this year, when Kim Jong Un was threatening to launch missiles at Guam, caused the North Korean leader to back down.

"The unpredictability of President Trump worked to some extent," Thae said. "But now I think that kind of exchange of rhetoric, warnings or whatever, are not necessary, and the most important thing is to deliver the policy messages towards North Korea."

The West must continue to make clear, he told Amanpour, that North Korea will never be accepted as a nuclear state.

"The US and West should continue the current momentum of maximum pressure and sanctions. But in the meanwhile the West and the US should try every possibility to open the dialogue with North Korea in order to tell North Korea that they would be destroyed if they continue" in the current direction.

CNN's Will Ripley and Tim Schwarz contributed to this report.

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