A North Korean spy chief has fled Kim Jong-Un's secretive state and defected to the South, officials in Seoul have said.

The army colonel had handled spy operations targeting South Korea at the North's General Bureau of Reconnaissance and is the highest-level military official ever to defect, a Seoul government official told the Yonhap news agency.

Unification and defence ministry spokesmen confirmed the report to AFP, but declined to elaborate on details including the official's name.

He is already believed to have passed on valuable intelligence about North Korea's spying operation against the South.

The latest blow to dictator Kim Jong-Un's authority comes days after the mass defection of 13 workers in a State-run restaurant in China.

The group switched sides after watching TV and surfing the internet alerted them to Pyongyang's propaganda.

The defections come at a time of elevated military tensions on the divided Korean peninsula.

North Korea has defied the international community with a series of missile tests in 2016 - and last week claimed to have successfully tested an engine for an intercontinental ballistic missile.

Meanwhile, Pyongyang has condemned Seoul and Washington for a sanctions drive at the United Nations (UN) over its nuclear and missile programmes, while also lashing out at the annual US-South Korea military war games.

Nearly 30,000 North Koreans have fled poverty and repression, despite risk of imprisonment and torture if caught, and settled in the South.

But the number of defectors - who once numbered more than 2,000 a year - has nearly halved since leader Kim Jong-Un took power after the death of his father and longtime ruler Kim Jong-Il in December 2011.