In South Korea, the country remains at a high alert level, just below a state of all-out war. South Korean officials have promised "enormous retaliation" if further provoked.
A White House official told ABC's Jake Tapper that the United States is discussing a number of measures with its allies, including action at the United Nations Security Council and further sanctions, and more joint U.S.-South Korea military exercises, to demonstrate solidarity and support.
The United States currently has 28,000 troops in South Korea.
Late last night, it was announced that starting next week, Nov.28 through Dec. 1, the USS George Washington and four other Navy ships will participate in military exercises with South Korea. The exercises were planned before the shelling attack and will take place in the Yellow Sea, west of the Korean peninsula.
In a statement from the U.S. Navy's Seventh Fleet, the military exercises are described as a measure to show the United States' "commitment to regional stability through deterrence."
The scene of yesterday's attack has been at the center of dispute where the two Koreas fought bloody skirmishes in 1999, 2002, and most recently November 2009. But this is the first time since the end of the Korean War in 1953 that North Korea has fired on South Korea's civilian territory.
U.N. Secretary General Ban Ki Moon called the attack one of "gravest incidents since the end of the Korean War" and said he "is deeply concerned by the escalation of tension on the Korean peninsula."
ABC News' Joohee Cho, Jake Tapper, Martha Raddatz, Alexander Marquardt, Kirit Radia, Luis Martinez and The Associated Press contributed to this report.