North Korean leader Kim Jong Un visits Farm No. 1116, under KPA (Korean People's Army) Unit 810, in this undated photo released by North Korea's Korean Central News Agency (KCNA) in Pyongyang on June 1, 2015. Reuters

Kim Jong Un is replacing North Korea's veteran military officers with defense chiefs closer to his age, reported Strategic Digest magazine Tuesday. The generational shift is the supreme leader's latest overhaul of the North Korean military amid reports that Kim, who is reportedly in his early 30s, has ordered the execution of various defense leaders.

Kim maintains "an extensive and capable internal security apparatus" to remove anyone who challenges his power, Strategic Digest noted. Last month, Kim publicly executed the country's defense minister after the regime accused him of treason, according to reports from South Korea. Hyon Yong Chol, a longtime Kim family loyalist, was reportedly executed with an anti-aircraft gun in Pyongyang.

In all, some 70 top leaders and more than 400 lower-level officials have been executed this year under Kim's orders, the Cato Institute, a right-leaning U.S. think tank, reported. "This brutality towards the power elite sets Kim apart from his father and grandfather. While Kim Jong Un’s apparent penchant for executions may reflect a peculiarly sadistic nature, it more likely grows out of insecurity ... Although there is no sign of organized resistance to the latest Kim, continuing turnover suggests that Kim is not, or at least does not see himself, as yet secure," wrote Doug Bandow, a senior fellow at the Cato Institute specializing in foreign policy and civil liberties.

North Korea released pictures of Kim Monday wearing a Panama hat as he oversaw fields and took a trip round the processing plant at a farm. The style choice was roundly lampooned by Western media outlets.

"North Korean internal politics is very volatile these days,” U.S. North Korea watcher Michael Madden recently told the Daily Express. “Internally, there does not seem to be any respect for Kim Jong Un within the core and middle levels of the North Korean leadership.”