"If the case is not resolved smoothly, it will have a devastating impact on South-North relations as well as US-North Korean relations," said the expert, Paik Hak-soon.
South Korea's Unification Ministry, which handles North Korea policy, said exchanges between local non-governmental groups and North Korea would continue despite the clash.
South Korea said two communist boats intruded up to 4.8km into South Korean waters, ignoring warnings to withdraw, broadcast from South Korean military boats with loudspeakers.
The clash occurred at 10:25am when South Korean navy vessels tried to repel two North Korean navy warships and an unspecified number of Northern fishing boats, the Southern military said.
A South Korean navy speedboat with 27 sailors aboard took a direct hit in its steering room from a heavy-caliber gun and caught fire. The South Korean military said a communist boat fired from about 500m away. The dead included a lieutenant and three enlisted men.
The South Korean military said 22 sailors were injured, but later revised the number to 20.
RSS