The United States and South Korea have begun their pre-planned joint military exercises off the Korean coast. They follow last week’s deadly bombardment by North Korea on a South Korean island.
Pyongyang has warned that it will carry out military attacks again if its territorial waters are violated.
Amid rising tension, an evacuation order was given to residents on Yeonpyeong Island before being withdrawn.
Some people were moved out of their homes, while others said they did not believe the North would start shelling again. But Pyongyang was reported to have deployed missiles near its disputed border with the South.
Four people died in last week’s shelling, which caused widespread damage.
North Korea has accused the South of using civilians as human shields. China has also warned against military acts near its coasts.
But the Pentagon says operations have taken place off the Korean coast for years, and the provocation comes from the North.