North Korea has fired artillery shells into South Korean waters, apparently in reaction to military exercises being conducted between the U.S. and South Korea.
Seoul responded immediately on Monday by shelling North Korean waters. Officials say no shells hit any land areas on either side along 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.
A White House official described the actions as "dangerous and provocative'', adding that the country's threats and provocations only isolate it further.
"We remain steadfast in our commitment [to] the defense of our allies and remain in close coordination with both the Republic of Korea and Japan,'' White House National Security Council spokesman Jonathan Lalley said Monday.
US-South Korea exercises
U.S. General Paul Kennedy says the joint exercises taking place about 360 kilometers north of Seoul have no political objectives.
"This exercise is not designed to act with any political situation. It's not designed to send a message. This is something that we have to do to interoperate with our allies," said Kennedy.
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.
Nuclear capabilities Malcolm Cook, an analyst at the Singapore-based Institute for South Asian Studies, tells VOA this could mean the North has developed the ability to build a nuclear warhead.
"Certainly, if they were able to show the capability of weaponizing, in that sense, their new nuclear capability, that would be a significant change to the inter-regional security picture in a significant way. The other thing they may do, are more underground tests or more than one test at other times. I think the range of what they call new nuclear measures is quite broad, but if they were able to show that they've been able to miniaturize a nuclear warhead to put on any of their short, medium or long range missiles, then that would be a significant change," said Cook.
Cook added that Monday's artillery exchange is not as serious as the deadly 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.