A South Korean navy ship issued a warning Thursday to a North Korean patrol ship that approached the Northern Limit Line (NLL), the de facto border in the Yellow Sea, near Yeonpyeong Island.
 
A military official said the South Korean navy vessel issued two warnings to the North Korean ship at around 10:40 a.m after the patrol ship came as close as three-point-six kilometers north of the NLL. The ship, however, retreated away from the maritime border.
 
The official said the patrol ship appears to have been monitoring North Korean fishing boats.