North Korea has replaced its hardline defence chief with a little-known army general, according to a state media report, in what outside analysts call an attempt to solidify Kim Jong-un's grip on the powerful military.

Jang Jong-nam's appointment is seen as the latest move by Kim aimed at trying to consolidate control since succeeding his late father in 2011. The announcement comes as tensions eased after weeks of warlike threats between North and South Korea, including vows of nuclear strikes from the North.

Pyongyang's rhetorical outbursts against massive US and South Korean war drills and UN sanctions over the North's February nuclear test were seen, in part, as a push to portray Kim at home as a respected military commander on the world stage.

Jang's new role as minister of the People's Armed Forces, however, is not thought to indicate a potential softening of Pyongyang's stance toward Seoul and Washington any time soon, analysts said. Jang replaces Kim Kyok-sik, the former commander of battalions believed responsible for attacks on South Korea in 2010 that killed 50 South Koreans. Outsiders do not know much about Jang, but analysts said it was unlikely that Kim Jong-un would name a moderate to the post at a time of tension with the outside world.

Mention of Jang's new role was buried in a state media dispatch listing those who attended an art performance with Kim Jong-un. It is not known exactly when Jang was formally appointed to the ministerial post.

The announcement coincided with the beginning of US and South Korean naval exercises involving a nuclear-powered US aircraft carrier on Monday. North Korea has criticised the carrier's inclusion in the drills, which it claims are preparations for an invasion of the North. Also, when tensions peaked in March, Washington took the unusual step of announcing that nuclear-capable B-52 and B-2 bombers had participated in the earlier, larger-scale joint drills between the allies. North Korea regularly cites the powerful US nuclear arsenal and Washington's deployment of those assets in the region as justification for its own pursuit of nuclear weapons.

One of the most notable changes from Kim Jong-un was the replacement of the powerful military chief Ri Yong Ho, who was dismissed because of what Pyongyang called an unspecified illness. Outside observers speculated that Ri, who held a different post from the one Jang has been appointed to, was purged as Kim tried to put his stamp on his government. Ri was also replaced by a little-known general.

State media previously identified Jang as head of the army's First Corps and said he pledged allegiance to Kim Jong-un and threatened South Korea in a speech last December. Jang was quoted as saying that his corps would annihilate its enemies and "turn each ravine into their death pitfall when the hour of decisive battle comes".

Kim Jong-un appears to be naming someone from a new generation to bolster his rule of the 1.2-million-member military, said Chang Yong Seok at the Institute for Peace and Unification Studies at Seoul National University.

Jang is believed to be in his 50s, while his predecessor is in his early 70s, according to Seoul's unification ministry, which is responsible for dealings with the North. Kim Kyok-sik was appointed to the ministerial job last year, but Chang portrayed him as belonging more to the era of Kim Jong-il.

Because outsiders know so little about Jang, it remains to be seen whether his appointment will lead to Pyongyang refraining from attacking South Korea, Chang said.

Another analyst, Cheong Seong-chang at the private Sejong Institute in South Korea, said it was unlikely that Jang was a moderate. Appointing a moderate as defence chief after weeks of high tension with the outside world could trigger whispers at home that the North was surrendering to Seoul and Washington, he said.