Yeonpyeong Island, South Korea: People on a South Korean border island were briefly ordered to shelter in bunkers on Sunday after explosions were heard from the direction of North Korea, officials said.
Faint sounds of explosions - possibly artillery fire - were heard several times from the North's mainland, a defence ministry spokesman said.
South Korea's military says that the sound of artillery was heard on Yeonpyeong Island.
South Korea's Joint Chiefs of Staff said that one artillery round was heard on Sunday from a North Korean military base north of the sea border dividing the two Koreas. It was not immediately clear where the round landed.
People on Yeonpyeong island, which was hit by deadly North Korean shellfire five days ago, were ordered to take shelter for 40 minutes, a witness said.
Dozens of reporters, along with soldiers and police and a few residents, headed for the bunkers.
"The order was lifted when no more sounds were heard," the spokesman said.
Tensions are acute after US and South Korean forces earlier on Sunday launched a major naval exercise, designed as a show of force to the North.
Puongyang has said "no one can predict the ensuing consequences" if the US aircraft carrier George Washington, the flagship of the drill, enters the Yellow Sea.
The fleet is manoeuvring at least 120 km south of the disputed inter-Korean border.
The sound of artillery fire from the North was also heard last Friday, but no shells landed in the South's waters.
Hundreds of residents fled the island in the days after the November 23 bombardment, leaving only a few dozen villagers still living there.
Four South Koreans died last week after the North rained artillery on the small Yellow Sea island, which is home to both fishing communities and military bases.
