A senior North Korean spy has defected to South Korea, South Korean officials confirm.

The officer has not been named, but the defense ministry in Seoul said he was a senior colonel in the Reconnaissance General Bureau and left in 2015.

Announcement of defection follows revelation that 13 North Koreans believed to have been working in China had also fled to South Korea. It was the largest group defection since North Korea’s leader, Kim Jong-un, took power in late 2011. South Korean media reported that the restaurant is located in the eastern city of Ningbo.

South Korea’s Yonhap news agency quoted a source as saying the colonel was seen as an elite among other defectors.

The colonel worked for the North Korean military’s general reconnaissance bureau before defecting, according to Seoul’s defense ministry and unification ministry. Both ministries refused to provide further details including a motive for the defection.

The reconnaissance agency was believed to be behind two deadly attacks blamed on Pyongyang that killed 50 South Koreans in 2010.

There have been occasional reports of lower-level North Korean soldiers defecting but it is unusual for a colonel to flee to South Korea.

More than 29,000 people have fled North Korea since the end of the Korean War, but high level defections are rare.

Some more senior figures have also fled while working overseas.

Defense Ministry spokesman Moon Sang-gyun said South Korea could not release further information on the colonel.

One unnamed official told Yonhap the man was the highest-level military official ever to have defected.

“He is believed to have stated details about the bureau’s operations against South Korea to the authorities here,” said the official.

The Reconnaissance General Bureau handles intelligence gathering and spying operations, as well as cyber warfare, said Yonhap.

The highest-level North Korean who took asylum in South Korea has been Hwang Jang-yop, a senior ruling Workers’ party official who once tutored Kim’s late dictator father, Kim Jong-il. His 1997 defection was hailed as a coup by many South Koreans and a clear sign that North Korea’s political system was inferior to the South’s.

Hwang Jang-yop died in 2010.