North Korea fired dozens of artillery shells onto a South Korean island on Tuesday, killing one person, setting homes ablaze and triggering an exchange of fire as the South's military went on top alert.
In what appeared to be one of the most serious border incidents since the 1950-53 war, South Korean troops fired back with cannon, the government convened in an underground war room and "multiple" air force jets scrambled.
The firing came after North Korea's disclosure of an apparently operational uranium enrichment programme -- a second potential way of building a nuclear bomb -- which is causing serious alarm for the United States and its allies.
Some 50 shells landed on the South Korean border island of Yeonpyeong near the tense Yellow Sea border, damaging dozens of houses and sending plumes of thick smoke into the air, YTN television reported.
One South Korean marine -- part of a contingent based permanently on the frontline island -- was killed and 13 other marines were wounded, the military said. YTN said two civilians were also hurt.
"The United States strongly condemns this attack and calls on North Korea to halt its belligerent action," the White House said in a statement.
"The United States is firmly committed to the defense of our ally, the Republic of Korea, and to the maintenance of regional peace and stability," the White House said, adding that it was in close and continuing contact with South Korea over the situation.
A U.S. official, speaking on anonymity, told Reuters that U.S. forces in Korea were closely monitoring the situation. But no U.S. troops were involved in the response to the North's artillery fire, the official said.
There are around 28,000 U.S. forces stationed in South Korea.
UPDATE III: Video from CNN.
UPDATE IV: South Korea vows an "enormous" retaliation if attacked again; Fox News reports say President Obama was pulled out of bed in the middle of the night as the crisis unfolded. Obama has reportedly spoken by phone with South Korean President Lee Myung-bak earlier this morning.
UPDATE V: Are Iran and North Korea collaborating on illegal weapons programs? (It's almost is if they're an axis of evil, or something).
UPDATE VI: Obama is "outraged." Very strong language from the White House. Gibbs says US and South Korean leaders are in "close and constant contact."