North Korean leader Kim Jong-un will put his frontline troops on a state of war from 5 p.m. today, state media said on Friday, as tensions with South Korea rise following an artillery exchange along the western border.

North Korean soldierspatrolling the village of Panmunjo in the demilitarized zone (DMZ) (Photo: Reuters)

"As supreme commander of the Korean People's Army (KPA), Kim Jong Un ordered KPA units to be combat ready for surprise operations," KCNA news agency reported.

Earlier, the South Korean military on Thursday (August 20) responded with dozens of 155mm artillery shells toward the area where the North Korean army had fired, a move that increased tensions on the divided peninsula.

Washington called on Pyongyang to immediately stop "provocative" actions after the first exchange of artillery fire between the two Koreas since October 2014. Both sides said there were no casualties or damage on their territory.

North Korea did not return fire but warned Seoul in a letter that it would take military action if South Korea did not stop anti-Pyongyang broadcasts along the border within 48 hours, Reuters reported, citing a source in the South Korean Defense Ministry.

However, in another letter, Pyongyang said it was ready to resolve the issue even if it considered South Korea's broadcasts a declaration of war.

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