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(CNN) —  

North Korea’s top three military officials have been replaced ahead of an historic summit between leader Kim Jong Un and US President Donald Trump, according to multiple reports.

All three appear to have been replaced by younger Kim loyalists, part of an ongoing transformation of the country’s political and military establishment since the young leader took power in 2011.

US intelligence officials and country experts say they move seems to have been driven more by concerns about potential corruption, and Kim’s desire to maintain tight internal control, than any wariness about a coup attempt.

South Korea’s Yonhap news agency, citing an unnamed intelligence official, reported that defense chief Pak Yong Sik had been replaced by No Kwang Chol, while Ri Myong Su, chief of the Korean People’s Army (KPA) general staff, had been replaced by his deputy, Ri Yong Gil.

Army general Kim Su Gil’s replacement of Kim Jong Gak as director of the KPA’s general political bureau was previously referenced in North Korean state media, and confirmed Monday by South Korea’s Unification Ministry, which deals with North Korean affairs.

“All these (promoted) guys are top Kim Jong Un guys,” said Michael Madden, author of the highly respected North Korea Leadership Watch blog. “All three of them have held very sensitive and high level positions under Kim Jong Un, they’re very loyal (to him), and all have experience interacting with foreign delegations.”

The three men replaced, Pak, Ri and Kim, are 68, 81 and 77 years old respectively.

US officials believe Kim Jong Un’s decision to replace the three officials may have been driven by his concerns the three were in positions to corruptly take advantage of outside investment coming into North Korea.

Two US officials who monitor North Korea developments closely tell CNN that Kim is concerned that he could risk his own ability to control and oversee outside involvement if North Korea opens to foreign investment. Kim, officials say, is determined to ensure any economic advantage comes to him and his immediate family and loyalists.

Shoring up power

Madden said the reshuffling at the top of the North Korean military was likely done for a number of reasons, among them preparation for the Kim-Trump talks and future South Korean negotiations and exchanges.

But he also emphasized the economic aspects of Kim’s move. In particular, the military’s General Political Bureau (GPB) is responsible for auditing and overseeing the financial operations of the KPA, which controls a large number of trading corporations and other businesses which could be highly involved in any future inter-Korean trade or infrastructure projects.

Political commissars under the bureau are stationed throughout the KPA and can influence the army’s activity at all levels.

“(Kim) is not going to want these military commissars helping themselves to any of this assistance coming to the North,” Madden said. “That was a problem during the sunshine period, a lot of misappropriation and malfeasance.”

He added that the size and breadth of the GPB responsibilities is such that, more than any other North Korean organization, it presents the most realistic potential threat to Kim’s own power.

“From about June 2017 to earlier this year, the KPA general political bureau was under investigation by the (ruling Worker’s Party), the first time in 20 years that the GPB was under investigation,” Madden said.

By bringing the GPB firmly under the Party’s and his own control, Kim is likely looking to avoid a repeat of the extreme action he had to take against his uncle, Jang Song Thaek, early into his rule.

Jang, previously one of the most powerful men in North Korea, was purged and executed in 2013 after he reportedly built up an alternate power base to his nephew.

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Korea experts said Kim’s ouster of the three military officials likely wasn’t driven by fears they would topple him.

“I’d be cautious about saying the leadership shuffle is a sign of Kim’s weakness,” Jung Pak, a senior fellow at the Brookings Institution and a former deputy national intelligence officer in the Office of the Director of National Intelligence.

“It’s a sign he’s comfortable shuffling people around,” she said, adding that it’s also a way to consolidate influence and avoid the formation of other power centers.

“When you do lop off some senior officials … you create a whole different cohort of people who are loyal to you,” Pak said.

Both Pak and Bruce Klingner, senior research fellow for Northeast Asia at The Heritage Foundation’s Asian Studies Center, speaking at an event organized by the Foundation for Defense of Democracies, said that North Korea’s overlapping system of informants gives Kim an added element of safety.

A coup attempt “hasn’t happened because there are competing security services that report not only on citizens, but on each other,” said Klingner, a former CIA deputy division chief for Korea. “I think he’s pretty firmly in control” and the military purge “shows how confident he is.”

Singapore summit

Preparations are still underway for Kim and Trump’s summit in Singapore, the first time a sitting US President will meet the leader of North Korea.

Trump met with former North Korean spy chief Kim Yong Chol for about 90 minutes Friday – the highest-level North Korean official to visit the US in 18 years.

He stressed that the Singapore meeting is part of a “process” that will go on for some time: “I told them today, ‘Take your time. We can go fast. We can go slowly.’”

This is something of a change from Trump’s previous statements, which seemed to indicate he expected a deal to be signed in Singapore on denuclearization and other issues, and raised the possibility it may be more of a meet and greet between the two leaders.

South Korea’s Blue House on Monday quashed suggestions a formal end to the Korean War could be announced at the Trump-Kim summit.

Kim is unlikely to spend much time in Singapore. Sanctions make it very difficult for senior North Korean officials to travel overseas, and Madden said Kim will also not wish to impose too much of a burden on the Singapore government, which will have to deal with onerous security arrangements caused by both leaders’ presence in the city.

There has also been speculation Kim does not wish to leave North Korea for an extended period of time as this may encourage any remaining opponents to his rule to seize the opportunity to stage a coup.

In 1971, Idi Amin famously seized power in Uganda while President Milton Obote was in Singapore for a meeting of Commonwealth leaders.

Madden said any similar attempt to wrest power during the North Korean leader’s absence was unlikely, pointing to Kim’s previous trips to Beijing and Dalian in China, which went off without a hitch.

CNN’s Yoonjung Seo contributed reporting from Seoul, South Korea, and CNN’s Barbara Starr and Nicole Gaouette contributed reporting from Washington.