US President Barack Obama is "outraged" by the North Korean attack on a South Korean island and plans to call President Lee Myung-bak to reaffirm the US commitment to Seoul's defence, a spokesman said.
"The president is outraged by these actions," said Bill Burton, a White House spokesman. "We stand shoulder to shoulder with our ally in South Korea", dpa reported
The White House was still trying to arrange a time for Obama to telephone Lee, who has threatened to launch a massive retaliation if North Korean attacks persisted.
Two South Korean soldiers were killed, at least 13 were injured and four civilians were hurt by the shells that landed on Yeonpyeong island, 12 kilometres off North Korea's coast. South Korea returned fire in an exchange that lasted about an hour.
The United States has nearly 30,000 soldiers stationed in South Korea, a presence that has been in place since 1953, when the Korean War ended.