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SEOUL — A high-ranking officer from Kim Jong Un's military spy agency has defected, according to South Korea's government.

"Although I cannot provide details, I can confirm the ... defection," South Korean defense ministry spokesman Moon Sang Keun told a press briefing on Monday.

The incident occurred last year but had not previously been announced. Government officials in Seoul described the defector as a senior colonel in North Korea's General Reconnaissance Bureau but did not identify him by name.

"These workers ... discovered the fakeness about North Korean government propaganda and that helped them to decide on collective escape"

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The North set up the bureau in 2009, consolidating several intelligence agencies to streamline espionge operations aimed at the South. Its head, General Kim Yong Chol, is accused by the South of being behind a 2010 torpedo attack against the South that sunk a navy ship and killed 46 sailors. The North denies any responsibility for the sinking.

Cha Du Hyeogn, a North Korea expert at the Korean Institute for National Reunification in Seoul, said a senior colonel would be "the highest military ranking so far to have defected to South Korea since the Korean War" ended in 1953.

The Unification Ministry said that a North Korean diplomat based in Africa separately defected to South Korea last year. It didn't elaborate.

The highest-level North Korean who took asylum in South Korea is Hwang Jang-yop, a senior ruling Workers' Party official who once tutored Kim's late dictator father, Kim Jong Il. Hwang's 1997 defection was hailed by many South Koreans as an intelligence bonanza and a clear sign that the North's political system was inferior to the South's. Hwang died in 2010.

A photograph of Kim Jong Un made available by North Korea's state-run KCNA news agency on April 9, 2016. KCNA / EPA

The disclosure came three days after South Korean government confirmed the en masse defection of 13 North Korean workers from its overseas restaurant in the Chinese city of Ningbo.

"This is the first time when a group of North Korean workers from its overseas restaurants have defected as a group and our government has accepted [their defection] from humanitarian standpoint," said Jeong Joon Hee, the spokesman for South Korean Ministry of Unification during a rare press conference over the issue of defections. "These workers learned about the reality about South Korea through Korean television [programs], drama, movies and the Internet while living overseas and so discovered the fakeness about North Korean government propaganda and that helped them to decide on collective escape."

Defectors who flee North Korean leader Kim Jong Un's regime usually are debriefed before spending 12 weeks at Hanawon, a government-run resettlement facility aimed at helping them to adjust to life in South Korea.

More than 29,000 North Koreans have defected to South Korea since the end of the 1950-53 Korean War, according to South Korean government records.