North Korea's young dictator Kim Jong-un appears to have sacked a prominent senior army chief in a bit to tighten his grip over the military.

Kim Kyok-sik, 75, a hawkish general who was tied to the leader's father, has been reportedly replaced as head of the army's general staff by Ri Yong-gil.

Kim Kyok-sik's name has disappeared from the list of senior regime officials attending public events in recent weeks, leading to speculations that he has been purged.

His name vanished as state media announced personnel changes at a meeting of the powerful central military command.

Days after the meeting, Ri, believed to be in his 60s, was pictured at a football match with the insignia of a four-star general. He previously sported three stars.

"We're closely watching developments in the North, believing that Kim Kyok-sik has been replaced by Ri Yong-gil, the Army's general staff chief of operations," a South Korean government source told Chosun Ilbo newspaper.

Kim Kyok-sik was believed to be the mastermind behind the sinking of South Korean Navy corvette Cheonan and the bombardment of Yeonpyeong island in 2010.

His head is the latest to roll since Kim Jong-un started a substantial reshuffle of top brass after he took the reins when his father Kim Jong-il died in December 2011.

Chang Yong-seok of the Institute for Peace and Unification at Seoul National University said the sacking was in line with Kim's efforts to secure his leadership.

"This means Kim Jong-un has almost completed replacing old generals left over from his father's time with younger generals who are loyal to himself," Chang told AFP.

In October 2012, Kim Chol, vice-minister of the army, and other senior officers were reportedly executed by mortar fire for drinking alcohol during the mourning period of the late dictator's death.

At least 15 senior party, government, and military leaders have been purged by the young North Korean leader in the last two years, according to Chosun Ilbo.

It was recently reported that in the purging process he had stripped his own stepmother, Kim Ok, of her post as a senior official in the Workers' Party finance and accounting department.

The army chief's replacement came after the reported execution by firing squad of Kim Jong-un's ex-lover Hyon Song-wol.

The woman was machine-gunned along with a dozen singers and musicians for allegedly violating state pornography laws by filming themselves having sex and selling the videos.

Reports from the hermit nation are impossible to confirm and often suffer from South Korean sensationalism.