North Korean patrol boats have crossed the Northern Limit Line (NLL) four times this month.
 
South Korea's Joint Chiefs of Staffs (JCS) said in a report submitted to Saenuri Party Rep. Song Young-keun that the de facto maritime border had been breached on four occasions between last Thursday and Tuesday.
 
A JCS official said South Korea fired warning shots following a cautionary broadcast after a North Korean patrol boat crossed the NLL by about 200 to 300 meters on Thursday.
 
The official said the boats appear to have crossed while cracking down illegal Chinese fishing boats in the West Sea, noting that the infractions were not likely military provocations.