North and South Korea briefly exchanged artillery fire May 22 in waters along the disputed Northern Limit Line, or NLL, a maritime extension of the Demilitarized Zone in the Yellow Sea that North Korea considers illegitimate. According to South Korean reports, North Korean naval artillery shells fell near a South Korean patrol vessel near Yeonpyeongdo, a small island south of the NLL. South Korean ships responded with at least two shots fired into the water near a North Korean patrol boat. On May 20, South Korean ships fired warning shots at three North Korean patrol vessels that had reportedly crossed south of the NLL. On May 21, North Korea responded by issuing a statement condemning "firing at random" by the South Koreans, declaring that "all warships of the south Korean puppet navy, big and small, which recklessly maneuver in the sensitive waters of the southwestern front, hot spots, will become without exception targets of the direct sighting firing by all strike means." The May 22 shelling appears to be intended to reinforce that warning.
The North has long sought to remove the NLL, which geographically restricts the use of North Korea's only major southern deep-water port, Haeju. Over the past decade, there have been several skirmishes and clashes between the two Koreas over the NLL. These include exchanges of fire between ships, including the sinking of ships on either side; artillery exchanges, including the North Korean shelling of Yeonpyengdo; and the attack on the South Korean Navy Corvette ChonAn. In some ways, the maritime clashes are more constrained than any action along the land component of the Demilitarized Zone — they are less likely to be the first moves in a full-scale military assault and can therefore be managed with a less intense response. But the increased scale and tempo of attacks, and particularly the shelling of occupied islands, has led South Korea to adjust its rules of engagement and response to any North Korean action. The North has signaled that it is doing the same.
It is perhaps notable that the incident comes amid heightened attention to the Korean Peninsula. There have been reports circulating for weeks that North Korea is prepared for another nuclear test and that it is building up its rocket launching facilities. Meetings are planned between North Korea and representatives of the United States and Japan. China has urged the resumption of the stalled six-party talks, and Russia has stepped up economic cooperation with the North. With the greater attention, even small-scale, relatively routine exchanges of fire along the maritime border can draw disproportionate attention.