Military forces on the Korean Peninsula are on high alert after North Korea shelled a South Korean island early Tuesday.
It was the heaviest attack since the Korean War ended in 1953. North Korean artillery shells were fired on South Korea's Yeonpyeong island, killing at least two soldiers and setting dozens of houses on fire.
Video shows the moment the artillery hit the island. South Korea was carrying out an annual military exercise when North Korea protested and warned them to stop or face retaliation.
North Korea expert Gordon Chang says that the South's threats of retaliation will do little unless they start backing them up. Listen to his comments, following this report.
The South Koreans did not stop and the North Koreans retaliated. South Korea returned fire and scrambled its fighter jets.
The island houses about 1,000 South Korean Marines and about 1,500 civilians, mostly fishermen.
The attack occurred just days after three Stanford University scientists returned from a visit to North Korea's Tongbyon nuclear facility, reporting that North Korea's nuclear program was far more advanced than anyone had expected.
"This validates a long standing concern that we've had in respect to North Korea and its enrichment of uranium," said Adm. Mike Mullen, chairman of the U.S. Joint Chiefs of Staff. "It also continues to validate a country that is led by a dictator who constantly desires to destabilize the region."
"North Korea likes to use provocation as a way to coerce the United States and the world to get negotiations and even into giving North Korea things that they want," said Victor Cha, at Georgetown University.
South Korean President Lee Myung-bak warned that if North Korea attacks again, the South will unleash an "enormous retaliation."
Meanwhile, White House Press Secretary Robert Gibbs said the U.S. "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.