A senior official at the North Korean embassy in London has arrived in South Korea, the government in Seoul said, in one of the highest-ranking defections ever from the secretive communist state.
The 55-year-old diplomat, Thae Yong Ho, fled with his family and they are now under the protection of the government in South Korea, the Unification Ministry said Wednesday.
Thae, the number two in the London embassy, was disillusioned with the rule of North Korean leader Kim Jong Un, the ministry said.
It is unclear exactly how Thae, who had been living in London for many years, reached South Korea.
Ministry spokesman Jeong Joon Hee said the defection showed that "internal solidarity is weakening" in Kim's regime, according to Yonhap News Agency.
The defection is likely to strain already-fraught tensions between South and North Korea. The two sides are officially still at war since the Korean War in the 1950s ended in a truce rather than a peace deal.
North Korea carried out an atomic test in January, and in recent months fired several mid-range missiles, including a ballistic missile that landed in the sea off the Japanese coast.
In July, South Korea and the US announced the deployment of the advanced missile defence system in South Korea, incurring the wrath of Pyongyang.
Many North Koreans flee the country each year because of famine and repression. Most cross the border into China or travel via other countries to South Korea.
In April, a group of 13 North Koreans who worked in the same restaurant in an unspecified country defected to South Korea.