A North Korean fishing boat crossed the inter-Korean maritime border in the Yellow Sea on Tuesday but retreated to its side following warnings from the South Korean Navy.

According to the Joint Chiefs of Staff, a North Korean fishing boat crossed some 500 meters over the western sea border east of the South's Yeonpyeong Island at 12:30 a.m. on Tuesday.

But the boat returned to the North 30 minutes later after having been warned by the South Korean Navy.

A military official said the North Korean fishing boat might have crossed the sea border unknowingly while fishing.

On Saturday, two North Korean patrol ships crossed the western maritime border and retreated after having received warnings from the South Korean Navy.