According to Yonhap, which cited intelligence sources, the chief of the general staff Ri Myong-su has also been replaced by his deputy, Ri Yong-gil.

And defence minister Pak Yong-sik has been succeeded by No Kwang-chol, previously first vice-minister, it added.

The wholesale reshuffle would be unusual if confirmed, Seoul’s unification ministry said.

“We will monitor related developments,” ministry spokesman Baik Tae-hyun said.

Pyongyang’s military, known as the Korean People’s Army, is immensely influential in the North and a centre of power in its own right, symbolised by the way Kim Jong-un is habitually flanked by generals on one side and civilians on the other when attending major ceremonial events.

According to researchers at NK Leadership Watch, the change at the top of the GPB “represents a continuation of tightening Party control over the KPA”.

The political bureau could be in a position to resist policy decisions by the leadership or try to profit from future South Korean economic aid, it said.

But new GPB director Kim Su-gil was a “highly trusted” lieutenant of leader Kim Jong-un, it added, who appointed him to the Pyongyang party committee – once a power base for his uncle Jang Song-thaek – after having the older man executed for treason in 2013.

Reports said the wider changes could be aimed at preventing objections in the North’s senior military ranks to any sudden changes in the country’s nuclear policy.

No Kwang-chol, the new defence minister, was known as a “moderate”, Yonhap cited the intelligence source as saying.

“The North appears to have brought in new figures … as the previous officials lacked flexibility in thinking,” the source said.

Analysts said the shake-up allowed Kim and the ruling party to tighten control over the KPA at a critical time of international engagement and domestic development.

“If Kim Jong-un is set on making peace with the US and South Korea and dealing away at least part of the nuclear programme, he will have to put the KPA’s influence in a box and keep it there,” said Ken Gause, director of the International Affairs Group at CNA, a non-profit research and analysis organisation.

“This reshuffle has brought to the fore the officers who can do just that. They are loyal to Kim Jong-un and no one else.”

Given the military’s secondary role in the country’s nuclear and missile programmes, the moves are likely more about installing a younger, even more trusted cohort of officials who Kim Jong-un can rely on as he confronts a variety of domestic and international issues, said Michael Madden, a North Korea expert at Johns Hopkins University’s 38 North website.

“The nuclear weapons are a side issue,” he said.

All of the newly promoted officials are younger than their predecessors, according to Yonhap, especially 63-year-old Ri Yong-gil, who is 21 years younger than Ri Myong-su.

“This points to two things: the consolidation of Kim Jong-un’s power as the sole leader of North Korea and strengthened cooperation between the North’s party and military as the country works towards further economic development,” said Yang Moo-jin, professor at the University of North Korean Studies in Seoul.

“They’re all young but capable people,” Yang said.

Lower-level US-North Korean talks to prepare for the summit are continuing but have made only “halting progress”, according to a second US official briefed on the discussions.

That official said US negotiators’ efforts to press for definitions of immediate, comprehensive, verifiable and irreversible denuclearisation by North Korea had run into opposition from the White House.

In a remarkable shift in tone eight days after cancelling the summit, citing Pyongyang’s “open hostility”, Trump welcomed North Korea’s former intelligence chief, Kim Yong-chol, to the White House on Friday, exchanging smiles and handshakes.

Yonhap reported that Kim Yong-chol had transited Beijing on Monday on his way back to Pyongyang from the United States.

Agence France-Presse, Reuters, The Washington Post