North Korea test-fired three short-range missiles off its east coast this week in an apparently routine exercise, a South Korean official said Friday.

The North lobbed what appeared to be KN-02 missiles with a range of 120 kilometers (75 miles) into the Sea of Japan (East Sea) on Wednesday, the defence ministry official said on condition of anonymity.

The North frequently conducts such short-range tests but their timing sometimes coincides with periods of tension.

It reportedly test-fired two short-range missiles off its east coast on December 19, the same day it announced the death of leader Kim Jong-Il.

Kim's son Jong-Un has been proclaimed supreme leader and has been officially appointed commander of the 1.2-million-strong military.

The North has stressed that its stance will not change under its new young chief and that the "songun", or military-first, policy will continue.

On Sunday state media showed Jong-Un driving a tank and giving orders to artillery, navy and air force units, in an apparent attempt to bolster his credentials with the world's fourth-largest armed forces.

The following day the military held a mass rally and vowed to become human "rifles and bombs" to protect him.