US explains the ship sinking as an 'unprovoked and unwarranted act of agression'. The White House called the attack "a challenge to international peace and security and a violation of the armistice agreement" which ended the 1950-53 war.
US Defense secretary Robert Gates informed that Pentagon was in a 'close discussion' with South Korea regarding the matter but it was up to them to decide how best to proceed.
US also informed that more than 30,000 American troops in South Korea were on a 'normal' state of readiness and were operating 'routinely' as of now. US also warned North Korea that they are an ally and friend of South Korea and will support the nation whatever their choice is.