SEOUL (REUTERS, BLOOMBERG, AFP) - North and South Korea exchanged gunfire around the South's guard post in the demilitarised zone (DMZ) between the two countries early on Sunday (May 3), raising tension a day after North Korean leader Kim Jong Un ended an almost three-week absence from public life with state media showing him visiting a factory.

Multiple gunshots were fired from North Korea at 7.41am local time towards a guard post in South Korea that borders the North, the South's joint chiefs of staffs said in a statement.

South Korea responded by firing two shots towards North Korea. No injuries were reported.

The South Korean military later said the North Korean gunshots were "not deemed intentional", according to the Yonhap news agency.

The two sides are now in talks via a military communication line, Yonhap News reported.

US Secretary of State Mike Pompeo said the shots fired from North Korea were believed to have been "accidental".

"Handful of shots came across from the north, we think those were accidental," he said on ABC's This Week.

"South Koreans did return fire. There was no loss of life on either side," he added.

After weeks of intense speculation about Kim's health and whereabouts, the country's official media published photographs and a report on Saturday that Kim had attended the completion of a fertiliser plant, the first report of his appearance since April 11.

Kim was seen in photographs smiling and talking to aides at the ribbon-cutting ceremony and touring the plant. The authenticity of the photos, published on the website of the official Rodong Sinmun newspaper, could not be verified.

The exchange of gunshots was the latest confrontation between the rival Koreas that technically remain at war.

In a lengthy briefing held later on Sunday, an official at South Korea's JCS said the gunshots did not seem a planned provocation, as the area where it occurred was farmland, but declined to provide a clear conclusion about the incident.

"In absence of vision (for the target) and in the fog, would there be an accurate provocation?" the official said.

Choi Kang, vice president of the Asian Institute for Policy Studies, says the timing of the 'grey area' provocation shows Kim is still in charge of the North Korean military.

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

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

Ewha University international affairs professor Leif-Eric Easley in Seoul said the shooting incident could be aimed at boosting morale in the North Korean military.

"The Kim regime may be looking to raise morale of its frontline troops and to regain any negotiating leverage lost during the rumour-filled weeks of the leader's absence," said Easley.

"South Korea and the United States should not take lightly such North Korean violations of existing military agreements."

The two Koreas have previously exchanged fire within the heavily-fortified DMZ, including in 2014 when Kim was unseen in public for more than a month.

Hundreds of thousands of troops on both sides of the border guard the DMZ that bisects the peninsula, a legacy of the 1950-53 war that ended in a truce rather than a peace treaty.

Despite its name, the DMZ is one of the most fortified places on earth, replete with minefields and barbed-wire fences.

Easing military tensions on their border was one of the agreements reached between Kim and South Korean President Moon Jae-in at a summit in Pyongyang in September 2018.

But most of the deals have not been acted on by North Korea, with Pyongyang largely cutting off contact with Seoul.

North Korea's discussions with the United States over Pyongyang's nuclear arsenal are also at a standstill, despite three meetings between Kim and US President Donald Trump.