A South Korean official says that North Korean leader Kim Jong-un did not undergo surgery during an almost three week absence from public life, a South Korean official said after the two nations exchanged gunfire at the demilitarized zone (DMZ) separating the two sides.

The Government official declined to provide reasons, but said speculative reports that Mr Kim had had an operation, citing some differences in his leg movements, were untrue.

Asked if media reports of Mr Kim having undergone a simple medical treatment were also untrue, the official simply said: "Yes."

North and South Korea exchanged gunfire around a rural guard post, raising tension a day after North Korean state media showed Mr Kim visiting a factory, the first report of him making a public appearance since April 11.

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After weeks of intense speculation about Mr Kim's health and whereabouts, which included one report he had undergone cardiovascular surgery, North Korea's official media published photographs and a report on Saturday that Mr Kim had attended the completion of a fertiliser plant.

Mr Kim was seen in photographs smiling and talking to aides at the ribbon-cutting ceremony and touring the plant.

State TV footage showed Mr Kim's leg movements appearing stiff and jerky.

The authenticity of the photos, published on the website of the official Rodong Sinmun newspaper, could not be verified.

Reclusive North Korea for years pursued nuclear and missile programmes in defiance of UN Security Council sanctions.

Talks between North Korea and the United States, highlighted by three meetings between Mr Kim and US President Donald Trump, are at a standstill.

Multiple gunshots fired in DMZ

Shots fired by North Korea across its border with South Korea were likely "accidental," US Secretary of State Mike Pompeo said on Sunday.

North and South Korea on Saturday exchanged gunfire around a rural guard post, raising tension a day after North Korean state media showed Mr Kim visiting a factory, the first report of him making a public appearance since April 11.

South Korea responded to shots fired from across the DMZ but no casualties were reported.

The exchange of gunshots on Sunday was the latest confrontation between the two Koreas that technically remain still at war after their 1950-53 conflict ended in a truce, not a treaty.

In a lengthy briefing held later on Sunday, an official at South Korea's JCS said the gunshots did not seem to be a planned provocation.

The US-led UN Command, which oversees affairs in the heavily fortified DMZ, said it was working with the JCS to assess the situation.

"The UNC will conduct a thorough investigation tomorrow to determine if there was an Armistice Agreement violation, and will provide the report to the appropriate authorities once completed," it said.

Choi Kang, vice-president of the Asian Institute for Policy Studies, said he believed the timing of the provocation shows it could have been planned to show that Mr Kim was still in charge of the North Korean military.

"Yesterday, Mr Kim was trying to show he is perfectly healthy, and today, Mr Kim is trying to mute all kinds of speculation that he may not have full control over the military," Mr Choi said.

"Rather than going all the way by firing missiles and supervising a missile launch, Mr Kim could be reminding us, 'yes I'm healthy and I'm still in power'."

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ABC/Reuters