Security personnel patrol outside Shangri-la Hotel during the IISS Shangri-la Dialogue in Singapore June 1, 2018.
The military moves also may be viewed as another step by Kim to underscore his willingness to make bold internal changes ahead of the scheduled June 12 summit with Trump in Singapore.
The announcement was made in the government's online gazette.
Ken Gause, director of the International Affairs Group at CNA, said: "If Kim Jong Un is set on making peace with the United States 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".
"We will continue to implement all UN Security Council resolutions on North Korea", Defense Secretary James Mattis said in Singapore. The United States is seeking a negotiated end to North Korea's nuclear weapons program.
"Singaporean Defense Minister Ng Eng Hen said his country was eager to pick up the bill for some of the summit costs to ensure the success of the meeting", the Washington Post reported.
Citing an unnamed intelligence official, Yonhap said No Kwang-chol, first vice minister of the Ministry of People's Armed Forces, had replaced Pak Yong-sik as defence chief, while Ri Myong-su was replaced by his deputy, Ri Yong-gil.
It is not clear what either side is prepared to offer during the negotiations.
Kim Jong Un is also likely expecting to receive more worldwide economic aid and investment soon as part of the ongoing talks and he wants to prevent corruption that plagued some past projects, Madden said.
Trump initially called for a quick denuclearization process, saying a phased approach has not worked in the past.
Last Friday, Trump put the planned summit with Kim back on track after he canceled it on May 24, citing "open hostility" from the communist regime. We can go fast. Trump also insisted that he "never said it happens in one meeting".
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.
North Korea made no immediate reference to any military changes, and it remains hard to assess whether the shake-up could signal a significant change in North Korean policies. "However, some of North Korea's measures it has taken give us reason to be positive", he said.