Media reports on the defection of a North Korean counsellor of political affairs in Cuba were true, the National Intelligence Service said.
A brief statement on Tuesday by the IS public affairs office gave no further details.
South Korea's mass-circulation Chosun Ilbo newspaper reported that diplomat Ri Il-kyu fled to South Korea with his wife and children in November.
Chosun Ilbo cited Ri, 52, as telling the newspaper he had decided to defect because of what he called disillusionment with North Korea's political system, an unfair job evaluation by Pyongyang's foreign ministry, and the ministry's disapproval of his hopes to visit Mexico to treat his neural damage.
He said hospitals in Cuba did not have the necessary medical equipment to treat his health problem due to international sanctions.
Other South Korean media outlets carried similar reports later Tuesday.
Ri defected before South Korea and Cuba established diplomatic ties in February, an event experts say likely posed a political blow to North Korea, whose diplomatic footing is largely dependent on a small number of Cold War-era allies such as Cuba.
Ri had been engaged in efforts to block Cuba from opening diplomatic ties with South Korea until his defection, the Chosun report said.
Ri won a commendation from leader Kim Jong-un for his role in negotiations with Panama that led to the release of a ship detained in 2013 for allegedly carrying banned items like missiles and fighter jet parts.
Ri was then a third secretary of the North Korean embassy in Cuba, the report said.
The number of highly educated North Koreans with professional jobs escaping to South Korea has steadily increased in recent years, the South Korean government says.
But it is still unusual for a member of the North's ruling elite to come to South Korea.
About 34,000 North Koreans have defected to South Korea to avoid economic hardship and political suppression since the end of the 1950-53 Korean War.
A majority of them are women from the North's poorer northern regions who arrived in South Korea since the mid-1990s, when North Korea suffered a devastating famine that was estimated to have killed hundreds of thousands of people.
South Korea's unification and foreign ministries said they could not confirm reports about Ri's defection.
The last such known high-profile defection to the South was that of Tae Yong-ho, a former North Korean deputy ambassador to the United Kingdom, in 2016.
The highest-level North Korean to seek asylum in South Korea is Hwang Jang-yop, a senior ruling Workers' Party official who once tutored Kim Jong-un's late father, dictator Kim Jong-il.
Hwang's 1997 defection was hailed by many South Koreans as an intelligence bonanza and a sign the North's political system was inferior to the South's. Hwang died in 2010.
with Reuters
