The White House on Tuesday condemned North Korea's, the latest in a series of provocations that have reawakened concerns about the threat posed by the communist country and its reclusive leadership.
In a statement released before dawn, Press Secretary Robert Gibbs called on North Korea to "to halt its belligerent action and to fully abide by the terms of the armistice agreement," the 1953 pact that ended the Korean War.
North Korea fired barrages of artillery onto a South Korean island near their disputed western border Tuesday, setting buildings ablaze and killing at least two marines after warning the South to halt military drills in the area, South Korean officials said.
Gibbs said the White House "is in close and continuing contact" with the South Korean government.
"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," he said.
A senior administration official said President Barack Obama was woken up shortly before 4 a.m. by National Security Adviser Tom Donilon, who updated the president on the situation. Mr. Obama will get further updates during his daily intelligence briefing before heading to Indiana, where he's scheduled to make remarks on the economy.
None of the more than 28,000 U.S. troops stationed in South Korea were involved in the military drills, said Lt. Col. Mark Ballesteros, a Pentagon spokesman in Washington.
U.S. troops have participated in the annual exercise in the past, said Marine Col. Dave Lapan, another Defense Department spokesman at the Pentagon. An earlier plan to have U.S. Marines participate in a landing maneuver with the South Koreans this year didn't work out because of American scheduling issues, Lapan said Tuesday.
The attack came amid high tension over North Korea's claim that it has a new uranium enrichment facility and just six weeks after North Korean leader Kim Jong Il unveiled his youngest son Kim Jong Un as his heir apparent.
On Monday, State Department spokesman P.J. Crowley told reporters the administration is studying the evidence a group of visiting American scientists used to conclude the North was building the enrichment facility, which presumably could be used to produce fuel for nuclear weapons.
"We will not be drawn into rewarding North Korea for bad behavior," he said. "They frequently anticipate doing something outrageous or provocative and forcing us to jump through hoops as a result. We're not going to buy into this cycle."
The North's artillery on Tuesday struck the small South Korean-held island of Yeonpyeong, which houses military installations and a small civilian population and which has been the focus of two previous deadly battles between the Koreas.
CBS News correspondent Celia Hatton reports that the island's roughly 1,200 residents took cover as the shelling continued for about an hour.
South Korea returned fire and dispatched fighter jets in response, and said there could be considerable North Korean casualties as troops unleashed retaliatory fire. The supreme military command in Pyongyang threatened more strikes if the South crossed its maritime border by "even 0.001 millimeter," according to the North's official Korean Central News Agency.
Earlier this month, during a speech to U.S. troops stationed in South Korea, Mr. Obama said: "Pyongyang should not be mistaken: The United States will never waver in our commitment to the security of the Republic of Korea. We will not waver."