South Korea's military has begun a major live-fire exercise amid high tensions following North Korea's deadly bombardment of a border island last month.
The Joint Chiefs of Staff say the firing exercises by warships or artillery units on land started in 29 locations, including one of five frontline islands near the disputed Yellow Sea border with the North.
On 23 November, the North killed two civilians and two marines in an artillery attack on Yeonpyeong Island.
It said it was retaliating for a South Korean artillery drill that had lobbed some shells into waters it claims as its territory.
Yeonpyeong has been excluded from this week's five-day drill, but firing will take place off Daecheong Island, 80 kilometres to the west.
It was unclear whether the firing would be into waters claimed by the North, which refuses to accept the Northern Limit Line sea boundary drawn by United Nations forces after the 1950-53 war.
Pyongyang has described the latest drill as an attempt to trigger a war.