North Korea recently ordered all its diplomats overseas to return their children home if they are aged 25 or older, according to the National Intelligence Service (NIS).
This is probably why a London-based senior North Korean diplomat, Thae Yong-ho, decided to defect to South Korea, sources said.
According to the sources, the spy agency told the National Assembly Intelligence Committee, Monday, that Pyongyang has ordered all diplomats' children aged 25 and over to come home, in an apparent bid to block potential defections by its officials.
The comment came after the Ministry of Unification confirmed last week that Thae, who was a deputy ambassador at the North Korean embassy in Britain, recently entered South Korea with his wife and children.
Thae became one of the highest-level North Korean officials to escape the repressive regime.
Sources said Thae's two sons are thought to be 26 and 19, and it is believed that the order from the regime was the direct cause of his defection.
"Thae may have made the decision because of his children's future," a source said, citing the NIS report to the Assembly committee. "The order may have prompted Thae to defect."
The NIS also reported that Thae only has two sons, ruling out speculation that daughter was left behind in the isolated state.
On the suspicion that Thae was holding a significant amount of North Korean funds when defecting to the South, the NIS told lawmakers the diplomat was not in such a position to handle Pyongyang's state money.
The NIS said Thae is not the son of the late four-star general Thae Pyong-ryol, who helped the North's late founder, Kim Il-sung, in the anti-Japanese campaign.
Thae's wife, however, came from a family that has close ties with the Kim clan, the agency said.