North Korea's Army politburo chief Hwang Pyong-so was caught on state media footage looking petrified when he discovered he was walking ahead of leader Kim Jong-un during a military ceremony.

North Korea watchers say the footage, shot in late April around the time when Army chief Hyon Yong-chol was executed with a FLAK gun, demonstrates the atmosphere of fear pervading the upper echelons of the regime.

The state-run [North] Korean Central TV broadcast the footage on Sunday showing Hwang and Kim heading to take a photo after a military ceremony. It shows Hwang visibly startled after discovering he is inadvertently walking a step ahead of Kim.

Hwang quickly moves behind Kim and extends his arms to guide the North Korean leader ahead.

A source said, "There are rumors that Army Chief Ri Yong-ho was purged back in 2012, just after Kim stepped into power, because he stood in line next to Kim when they paid a visit to the Kumsusan Palace of the Sun," where the embalmed bodies of nation founder Kim Il-sung and former leader Kim Jong-il are displayed.

But other observers say such rumors are tittle-tattle and the purges are part of efforts to bring the unruly military under control.

