The South Korean coast guard said the bodies were found at the construction site of a marine corps base on Yeonpyeong Island, near the disputed maritime border between the Koreas, that was wracked Tuesday by North Korean artillery, the South Korean news agency Yonhap reported.
The civilian deaths brought the number of deceased in Tuesday's attack to four, including two marines, officials said. Eighteen others were wounded.
U.S. President Obama and South Korean President Lee Myung-bak agreed Tuesday to conduct joint military exercises as a first response to the attack, with the United States sending the aircraft carrier George Washington and other ships into the region, The New York Times reported.
Obama called Lee to tell him the United States "stands shoulder to shoulder with our close friend and ally," the White House said of the phone conversation.
The two presidents agreed to hold combined military exercises and enhanced training in the days ahead "to continue the close security cooperation between our two countries and to underscore the strength of our alliance and commitment to peace and security in the region," the readout said.
The decision to send the U.S. aircraft carrier came as the South Korean military was in "crisis status," the Times said. Lee said he would order strikes on a North Korean military facility if indications of new attacks were evident.
The military attack on the island came less than two weeks after North Korea invited a U.S. nuclear scientist to its Yongbyon nuclear site and showed him what was described as a new centrifuge plant that, if fully operational, should allow North Korea to enrich uranium into nuclear fuel.
"They have a 60-year history of military provocations -- it's in their DNA," a senior administration official told the Times. "What we are trying to do is break the cycle" of rewarding North Korea's belligerent behavior with "talks, inducements and rewards."