A top North Korean diplomat and his wife who defected to South Korea come from privileged backgrounds as they are descendants of prominent guerrillas who fought against Japanese colonialists in the 1930s, a source familiar with the matter said Thursday.

Thae Yong-ho, who served as minister at North Korea's embassy in London, is believed to be the son of late four-star general Thae Pyong-ryol who actively took part in the anti-Japanese campaign, led by North Korea's late founder Kim Il-sung, according to the source.

The North's diplomat Thae, his wife and children have recently defected to South Korea, making him one of the highest-level North Koreans to desert the repressive regime, South Korea's unification ministry said Wednesday. As minister, he was the No. 2 man at the diplomatic mission there.

"A North Korean diplomat usually works in overseas missions for three years, but Thae had worked in London for 10 years, mainly because of his good family ties," the source said.

Born in 1916, Thae's father, a former member of the ruling party's central committee, served as a general for the Korean People's Army (KPA) before his death in 1997.

O Hye-son, Thae's wife, is also known as a descendant of O Peak-ryong who also joined the anti-Japanese guerrilla activities with the communist country's founder, according to another source.

The senior O died at the age of 70 in 1984.

She is believed to be a close relative of O Kum-chol, vice chief of the KPA General Staff, who is the son of O Peak-ryong, it added.

Seoul's unification ministry declined to confirm the family background of Thae and his wife.

Thae's high-profile defection is seen as a sign that more North Korean elites may follow suit in the face of the iron-fist rule by North Korean leader Kim Jong-un and tougher international sanctions.

Seoul's unification ministry said that Thae defected to Seoul due to his disillusionment with the North's regime under the incumbent leader and aspiration for freedom. The diplomat may have chosen to defect for a better future for his children.

The 55-year-old Thae was known to have been in charge of promoting North Korea's national image in Britain in the face of international sanctions.

Foreign media reports said that he was scheduled to return to North Korea this summer after a 10-year-stay in London.

The South Korean government refused to unveil details over Thae including how and when his family came to South Korea.

A ministry official said that as Thae was exposed to various information outside North Korea, he might have realized that there is no hope in North Korea.

"I think that his defection may serve as a starting point in cracking internal solidarity in the Kim Jong-un regime," the official said, asking not to be named.

He said that what causes more North Koreans to escape their home country is becoming more varied at a time when some are seeking to defect to Seoul for a better life, not because of political persecution in the North.

Seoul said Thae, who was initially thought to have sought asylum in a third country, is one of the most senior North Korean diplomats to have defected to Seoul so far.

In 1997, Jang Sung-gil, the then North Korean ambassador to Egypt, sought asylum in the United States, with his elder brother, a North Korean diplomat based in France.

Thae's defection is widely expected to anger the North's leader, who has been strengthening his reign of terror by killing numerous government and military officials since taking power in late 2011, analysts said.

Analysts said that the diplomat's defection would have a psychological impact on the North's elite group, given his status, but its effect may not be large enough to rattle the North's regime.

"Thae might have had huge difficulty in doing his job to promote North Korea in the face of tough sanctions including Washington's blacklisting of the North's leader over human rights abuses," said Cheong Seong-chang, a senior researcher at the Sejong Institute.

Cheong said that his escape would have some impact in terms of agitating Pyongyang's elite members, but it is not likely to hit the North Korean regime hard as shown in the case of Hwang Jang-yop's defection. Hwang is the highest-ranking North Korean ever to defect to South Korea.

Hwang, who was said to have tutored former North Korean leader Kim Jong-il, defected to Seoul in 1997 after serving high-level posts in North Korea including a secretary of the ruling Workers' Party. He died in 2010.

Thae's defection came after a group of 13 North Koreans who worked at a restaurant in China run by North Korea defected to South Korea en masse in April. In June, three more North Korean restaurant employees working in China escaped to Seoul. (Yonhap)