How unusual is defection of North Korean colonel?

South Korea announced Monday that a colonel belonging to North Korea’s top spy agency had defected to the South, a rare public admission, especially for high-ranking officials.

The South’s Unification Ministry said the colonel, who belonged to the North’s General Reconnaissance Bureau, had arrived in South Korea last year, according to Yonhap, a South Korean news agency. Some other outlets in the country also reported that a North Korean diplomat who was based in Africa defected last May, The New York Times reported.

The defection is a coup for Seoul. The North set up the General Reconnaissance Bureau in 2009, consolidating several intelligence agencies to streamline operations aimed at the South, Reuters reports.

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.

The bureau is also known to operate an elite team of computer specialists working to infiltrate the networks of the South and other countries and to conduct cyber attacks against key institutions.

The news comes only days after South Korea revealed that 13 North Koreans who had been working in the same restaurant run by the North in another country – some reports suggested China – had defected to the South. The group defection was the largest since Kim Jong Un took leadership of the North in 2011.

Defections from North to South Korea are not uncommon, with more than 29,000 North Koreans having done so since the end of the Korean War in 1953. But while even some soldiers have been known to defect, it is more rare for figures as highly ranked as colonels to do so.

Even more unusual was the South’s swift announcement of such a high-level defection, the New York Times noted. Such announcements are usually only made once defectors have been thoroughly debriefed and when the government is relatively sure the safety of their families in the North won’t be jeopardized.

The timing of the announcement regarding the 13 defected restaurant workers led some members of the main liberal opposition Minjoo Party to accuse conservative President Park Geun-hye’s government of trying to win votes before Wednesday’s parliamentary elections.

To date, the highest level North Korean to take asylum in South Korea is Hwang Jang-yop, a senior ruling Workers' Party official who died in 2010. Hwang’s 1997 defection was seen by many South Koreans as a a boon for intelligence and as a sign the North’s political system was inferior, according to the Associated Press.

Some North Koreans who defect try to return home to visit or even re-defect to the North, despite the danger, because of their desire to reconnect with friends and family, the BBC reported.

Such North Korean expats often push for warmer relations between the two nations.