Some of the most notable clashes between N. Korean and S. Korean forces in recent years:

l Aug. 20, 2015: S. Korea fires dozens of artillery rounds across the border, saying N. Korea had fired first to back up a threat to attack loudspeakers broadcasting anti-Pyongyang propaganda. N. Korea says the S. Korean shells caused no injuries, but denies firing and responds with fury. The North later announces its frontline troops are in a “quasi-state of war” and orders them to prepare for battle.

l Oct. 10, 2014: North and South Korea trade machine-gun and rifle fire about two hours after S. Korean activists release anti-Pyongyang propaganda balloons across the border. Another exchange of gunfire comes nine days later. There are no reports of damages or injuries in either incident.

l Aug. 10, 2011: S. Korea fires several shells in what it says are two artillery exchanges with the North, which denies Seoul’s claim that it fired first. No one is hurt.

l Nov. 23, 2010: N. Korea bombards the front-line S. Korean island of Yeonpyeong, killing four S. Koreans, two of them civilians, in the first attack on a civilian area since the Korean War. The North said it was responding to S. Korean artillery exercises held earlier.

l March 26, 2010: The S. Korean warship Cheonan sinks near the western sea border; 46 sailors are killed and 58 rescued. Pyongyang continues to deny responsibility, though an international team of investigators concluded that a N. Korean submarine fired a torpedo that tore the ship in two.

l Nov. 10, 2009: A North Korean ship is heavily damaged near the western sea border in a two-minute skirmish with a S. Korean ship that was only lightly damaged. South Korean officials say a N. Korean officer was killed and three other sailors wounded, while the South suffered no casualties.

l June 29, 2002: The N. Korean navy sinks a S. Korean patrol boat in a clash along the contested western sea border. Six S. Korean sailors were killed, the North acknowledged an unspecified number of casualties and each side accused the other of triggering the 21-minute gun battle.

l June 15, 1999: In the first naval skirmish between the two Koreas since the Korean War, a gunbattle breaks out when S. Korean navy ships attempt to bump and push N. Korean patrol boats back to their own waters. About 30 N. Korean sailors were believed to have died when one of their torpedo boats was hit and sunk, while S. Korean sailors suffered only minor wounds.