Thae Yong Ho, North Korea’s deputy ambassador in London who has defected with his family, speaks on a podium in London, Britain in a still image taken on 17 August, 2016.

North Korea has branded its senior diplomat who defected to South Korea as human scum, claiming he is responsible for a series of crimes.

Thae Yong Ho became the highest-ranking North Korean diplomat to defect to the South, Seoul confirmed on Wednesday.

North Korean State media said Mr Thae had been ordered to return home in June to be investigated for a series of crimes, including embezzling government funds, leaking confidential secrets and sexually assaulting a child.

The Korean Central News Agency (KCNA) also denounced the British government for rejecting its demands to extradite Mr Thae back to the North.

KCNA said Mr Thae “should have received legal punishment for the crimes he committed, but he discarded the fatherland that raised him and even his own parents and brothers by fleeing, thinking nothing but just saving himself, showing himself to be human scum who lacks even an elementary level of loyalty and even tiny bits of conscience and morality that are required for human beings.”

It also accused Seoul of using his defection for propaganda aimed at insulting the North Korean leadership.

Seoul’s Unification Ministry said Mr Thae decided to defect because of his disgust with Kim Jong-un’s government, his yearning for South Korean democracy and worries about the future of his children.

More than 29,000 North Koreans have defected to South Korea since the end of the 1950-53 Korean War, according to the South Korean government. Many defectors have said they wanted to leave the North’s harsh political system and poverty. Pyongyang often accuses the South of deceiving or paying its citizens to defect, or claims that they have simply been kidnapped.

In April, 13 North Koreans working at a North Korean-operated restaurant in China defected to South Korea. It was the largest group defection since Kim Jong-un took power in late 2011. Later in April, South Korea also revealed that a colonel in North Korea’s military spy agency had defected to the South last year.

Most South Korean analysts say it’s premature to take the defections of Mr Thae and other senior officials as indicators that the unity of North Korea’s ruling elite is starting to crack because there are no significant signs that Kim Jong-un’s grip on power is weakening.

South Korea doesn’t always make high-level defection cases public. Its announcement of Mr Thae’s defection came with ties between the rivals at one of their lowest points in decades following the North’s nuclear test and long-range rocket launch earlier this year.

North Korea recently has expressed anger at a US plan to place an advanced missile defense system in South Korea. The North has warned of unspecified retaliation and fired several missiles into the sea earlier this month.