North Korea fired machinegun rounds into South Korea on Friday, prompting the South to retaliate with its own fire, the South's defence ministry said, three days after the rivals exchanged fire at a disputed sea border.
A ministry official said shots were fired at the border town of Yeoncheon, but added no one was hurt. South Korean activists had sent leaflets critical of the North Korean regime flying into the North from the town.
South Korea's military returned fire after hearing the sound of the North's machinegun fire, the official said.
North Korea on Thursday issued a statement saying if the South Korean allowed leaflet drops to continue, it would hurt inter-Korean ties, days after a high-level delegation visited the South and agreed to resume dialogue.
North Korea has reacted angrily to leaflet drops by South Korean private groups that carried messages attacking the authoritarian leadership in Pyongyang, vowing to attack them but has never taken action to follow up on the threat.
"This is the first time North Korea actually took an action against leaflets. It spilt cold water over the South-North relationship after the high-level delegation visit from North. It will strain the relations again." Yang Moo-jin, a professor at the University of North Korean Studies, said.
On Tuesday, a South Korean naval ship fired warning shots after a North Korean patrol boat crossed a disputed sea border off the peninsula's west coast and fired shots back before retreating, a South Korean defence official said.
There were no casualties on the South Korean side and none of the shots by either side was aimed at the other's vessel, he told Reuters.