A high-ranking North Korean diplomat based in London has defected to South Korea.

The Unification Ministry in Seoul said Wednesday that Thae Yong-ho, a minister at the North Korean embassy in London, recently arrived in the South with his wife and children.

Ministry Spokesman Jeong Joon-hee said that the 55-year-old diplomat is now under the protection of the South Korean government and that necessary steps are being taken in accordance with customary procedures of handling North Korean defectors.

The spokesman said Thae, the number two official at the North Korean embassy, is the highest-ranking North Korean diplomat ever to seek asylum in the South.

The BBC said earlier that the diplomat served as deputy to the North Korean ambassador and was responsible for promoting the image of his country to the British public.

As a motive for defection, the spokesman said the North Korean diplomat was disillusioned with the North Korean system and had yearned for South Korea's free democracy. He said concerns over his children's future were also a factor.

Thae’s defection comes amid growing speculation about instability within the North Korean society, fueled in part by a turnaround in the number of North Korean defectors.

The number of North Koreans defecting to the South had declined continuously for several years as its leader Kim Jong-un strengthened a crackdown on defectors. However, the number has increased by 15 percent in the first seven months this year compared with the same period a year earlier.

Even those with a promising future, prestige, or power in the North have begun defecting at an increasing rate. Reports indicate that a teenage prodigy attending a math Olympiad in Hong Kong, and a general-level military official are also planning to defect from the North.

Thae’s defection reinforces the trend, as he is reportedly from one of the most prestigious families in the North. According to local media reports, his father is Thae Byong-ryol, a resistant fighter that fought side by side with North Korean founder Kim Il-sung against the Japanese between 1910 and 1945. His wife is also known to be a daughter of another Korean resistance fighter.

Experts say the defection of those with such a prestigious background will further unsettle the society, which is already struggling due to the toughened international sanctions.

Meanwhile, the North Korean government has reportedly sent inspectors to monitor North Koreans working abroad to prevent further defection.