South Korea says its troops have exchanged fire with North Korea along their tense land border.
The military says in a statement South Korea fired two rounds in response after issuing a warning broadcast.
It said South Korea suffered no casualties.
The video of the inauguration of a factory from North Korea came to the media after it went missing for 20 days and claimed Kim Jong Un was completely healthy. But most of the deals have not been acted on by North Korea, with Pyongyang largely cutting off contact with Seoul.
The Koreas are split along the 155-mile long, 2.5-mile wide border called the Demilitarised Zone that was originally created as a buffer.
The South Korean official declined to provide reasons for believing that Mr Kim did not undergo surgery, but said speculative reports that he may have had surgery, citing some differences in his leg movements, are not true, Yonhap reported.
Speculation about Kim's health has been swirling since his conspicuous no-show at April 15 celebrations for the birthday of his grandfather, the North's founder - the most important day in the country's political calendar.
North Korean state media released this image they say is of leader Kim Jong-un at the fertiliser plant
The South Korean authorities made it clear that the incident is in violation of the bilateral military accord of the Comprehensive Military Agreement signed in September 2018, and urged the North to fully abide by the agreement.
Mr. Trump has continued to refer to Mr. Kim as a friend, but the mystery of the past three weeks has served to emphasize the limits of that relationship and his lack of progress in persuading North Korea to give up a weapons program that now threatens the United States.
Trump on Saturday welcomed the leader's return.
Medical experts told NK News, a US-based news outlet specialising in analysis of the hermit state, this mark on his arm, which was not seen during his last public outing on April 11, could be linked to a cardiovascular procedure.
He was with several senior officials, including his younger sister Kim Yo Jong, who is expected to take over if her brother is suddenly unable to rule.
"We are still hopeful that we'll find a path to negotiate that solution to get the outcome that is good for the American people, good for the North Korean people and for the whole world".
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