"The North appears to have brought in new figures amid the changes in inter-Korean relations and the situation on the Korean Peninsula as the previous officials lacked flexibility in thinking", the intelligence official told Yonhap, in particular identifying No Kwang-chol, the new defense minister, as a "moderate".
USA officials believe there was some dissension in the military about Kim's approaches to South Korea and the United States.
"I am going to visit the DPRK and meet HE Kim Jong-un", Assad was quoted saying in the report, using the initials for North Korea's official name and referring to Kim using letters that stand for "his excellency".
Would Trump or Kim be staying in the same hotels attendees were staying in - would they be eating from the same buffet breakfasts?
U.S. Defense Secretary Jim Mattis says worldwide sanctions on North Korea will only be lifted when Pyongyang takes concrete steps to dismantle its nuclear program.
The Trump administration wants the North to get rid of its nuclear arsenal, in return for relief from economic sanctions.
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. All the officials who were reportedly promoted were younger than those dismissed, according to Yonhap, including the new general staff chief, Ri Yong Gil, who at 63 is 21 years younger than the outgoing Ri.
Seoul's unification ministry has said the reshuffle would be unusual if confirmed.
Since the beginning of the year, Mr Kim has launched a flurry of diplomatic meetings with leaders in China and South Korea.
Lower-level U.S. -North Korean talks to prepare for the summit are continuing but have made only "halting progress", according to a second U.S. official briefed on the discussions. "North Korea will receive relief only when it demonstrates verifiable and irreversible steps to denuclearization".
Yonhap reported that Kim Yong Chol had transited Beijing on Monday on his way back to Pyongyang from the United States.
"If they think it enhances their legitimacy, then they certainly don't have a good understanding of the worldwide community, and certainly what the United States is going to think about it", he said.