The Institute for National Security Strategy, a South Korean think tank, released "The misgoverning of Kim Jong Un's five years in power" on Thursday, detailing how the North Korean leader uses executions to tighten his hold on power.
Of those killed, about 140 were senior officers in the country's government, military and ruling Korean Worker's Party.
RAND Corporation senior defense analyst Bruce Bennett told CNN Kim had shown an "extreme" level of brutality and ruthlessness since 2011.
"For example, in the five years he has served as leader of North Korea, he has purged (his) Defense Minister five times, while his father changed his Defense Minister only three times in his 17 years ... and two of those changes were because (they) died of old age," he said.
North Korea's bloody history
Although news rarely leaks from North Korea's authoritarian state, stories of Kim's brutal executions have sometimes filtered out over the past five years.
Earlier this year, North Korea's top education official Kim Yong Jin
was executed by firing squad after he exercised a "bad attitude" at the country's Supreme People's Assembly in June.
In May 2015, Kim had his Defense Minister Hyon Yong Chol
killed with an anti-aircraft gun at a military school in Pyongyang, in front of an audience.
"(It) would have torn his body apart," Bennett said. "And of course Kim made sure the Defense Minister's family was there to see the execution."
Two years earlier, in 2013, Kim Jong Un's uncle was executed for trying to overthrow the government, according to state media, which described him as a "traitor for all ages."
The "spoiled", "blunt" dictator
Hawaii Pacific University professor Seung-Kyun Ko told CNN Kim tended to be blunt and "a bit extreme" in response to perceived threats.
"During his upbringing, he has been spoiled because he was a son of Kim Jong Il. The major danger is there is no one in his leadership circle to restrain him," he said.
Ko said Kim was desperate to live up to the expectation that he would be a "great leader."
"To do so, he has been pushing around the top leaders -- military and civil, primarily the party -- to show off his being the boss," he said.