South Korean soldiers opened fire on North Korean troops at the border between the two countries on Thursday, just hours after Russian President Vladimir Putin had left Pyongyang.
The shots were fired after dozens of North Koreans crossed the famously dangerous border for the third time in three weeks.
South Korean soldiers warned the men to stop advancing with loudspeakers, but they only retreated when gunshots were fired.
The Demilitarised Zone (DMZ) divides the two countries who are still techically at war. The conflict between the North and the South ended in 1953 with an armistice but with no peace treaty.
South Korea has accused the North of laying down more mines by the border and building anti-tank barriers.
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The construction at the border along with the landmines appear to be attempts to stop North Korean defectors from escaping the country, analysts say.
A JCS official told the Daily Mail: “North Korea’s activities seem to be a measure to strengthen internal control, such as blocking North Korean troops and North Koreans from defecting to the South.”
Koh Yu-hwan, North Korean studies emeritus professor at Dongguk University, added: “By laying mines, North Korea is demonstrating once again that, as per the instructions of the supreme leader (Kim Jong Un), there will be no reconciliation with the South.
“North Korea is not laying mines across the entire frontline, but rather in areas that are easily observable by the South. They are also blocking roads and railways that were previously areas of inter-Korean cooperation.”
The rising tension comes as Russian President Putin visited North Korea on Thursday.
Putin and North Korean leader Kim Jong-un have strengthened their ties since Russia‘s invasion of Ukraine.
Moscow has been accused of sourcing weapons from Pyongyang to help with its war effort.
Kim said North Korea and Russia have a “fiery friendship” and promised “full support and solidarity to the Russian government, army and people in carrying out the special military operation in Ukraine to protect sovereignty, security interests and territorial integrity”.
They released a bizarre video of the two leaders driving in a limousine. Kim and Putin also exchanged gifts.
Putin gifted Kim a Russian Navy dagger and a tea set. Kim gave Putin some artwork, including one piece with Putin’s face on it.
South Korean President Yoon Suk Yeol’s office issued a statement after the visit: “It’s absurd that two parties with a history of launching wars of invasion – the Korean War and the war in Ukraine – are now vowing mutual military cooperation on the premise of a pre-emptive attack by the international community that will never happen.”