North Korea's top three military officials are believed to have been removed from their posts, as US President Donald Trump and North Korean leader Kim Jong Un prepare to meet on June 12 in Singapore.
A senior US official, who declined to be identified, quoted a report by South Korea's Yonhap news agency on Sunday which said all three of the North's top military officials were believed to have been replaced.
Trump on Friday revived the summit after cancelling it a week earlier. The United States is seeking a negotiated end to North Korea's nuclear weapons program.
US officials believe there was some dissension in the military about Kim's approaches to South Korea and the United States.
Yonhap identified the three officials as defence chief Pak Yong-sik, chief of the Korean People's Army's (KPA) general staff Ri Myong-su, and director of the KPA's General Political Bureau Kim Jong-gak.
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 said Army General Kim Su-gil's replacement of Kim Jong-gak as director of the KPA's General Political Bureau was confirmed in a North Korean state media report last month.
The White House, State Department, CIA and Office of the Director of National Intelligence did not immediately respond to requests for official comment.
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, afterward exchanging smiles and handshakes.