North Korea has fired artillery shells into South Korean waters, apparently in reaction to military exercises by the U.S. and South Korea.
Seoul responded immediately on Monday by shelling North Korean waters. Officials say no shells hit land on either side of the western sea boundary and no one was injured. South Korean officials said some residents of border islands were evacuated to shelters as a precaution.
U.S. General Paul Kennedy says the joint exercises taking place about 360 kilometers north of Seoul have no political objectives.
The North in recent weeks has increased threatening rhetoric and conducted a series of rocket and ballistic missile launches into waters off the east coast of the Korean peninsula.
Pyongyang threatened on Sunday to conduct what it called "a new form of nuclear test" after the U.N. Security Council condemned the North's recent ballistic missile launches.
Malcolm Cook, an analyst at the Singapore-based Institute for Southeast Asian Studies, tells VOA this could mean the North has developed the ability to build a nuclear warhead.
Cook says Monday's artillery exchange is not as serious as the sinking of a South Korean warship in March 2010, and North Korea's shelling of Yeonpyeong Island in November of that same year that killed four people.
A statement Sunday from the North's Foreign Ministry said it was intolerable that the Security Council would "turn a blind eye" to U.S. nuclear war exercises while denouncing the North Korean army's self-defensive rocket launch exercises.
After North Korea fired two medium-range ballistic missiles into the sea off the east coast of the Korean peninsula Wednesday, the Security Council condemned the launches the next day, saying they violated U.N. resolutions.
Pyongyang routinely calls military drills involving South Korea and the U.S. a rehearsal for invasion