The NKIS official elaborated on the response to the assassination based on a phone conversation with his North Korean acquaintance who made a business trip to Beijing earlier this week.

Pyongyang residents in their 50s and 60s know well of Kim Jong-nam, who had been once considered the successor to power, although they do not know about current leader Kim Jong-un's real brother, Kim Jong-chol, the official said.

"They think the murder of the eldest grandson of North Korea founder Kim Il-sung and the eldest son of the late leader Kim Jong-il is a thing that cannot happen," he said.

People thought that Jang Song-thaek deserved death for being a reactionary when he was executed by his own niece Kim Jong-un in 2013.

"But this time people are enraged by Kim Jong-un's murder of his own brother," he said.

A North Korean defector, who once worked in the North Korean Cabinet, also said every citizen in Pyongyang learned about the assassination in less than 10 days after it took place. (Yonhap)