The Korean Peninsula is one of the most fragile places on earth. Although an armistice ended open warfare between North and South Korea in 1953, a state of war still technically exists between the two nations.
In recent weeks, a number of incidents have threatened the tenuous peace, including the North's attack on the South Korean island of Yeonpyeong that left four people dead.
The situation has South Koreans fearing another war.
"It is the most threatening time after the South Korea-North Korea cease-fire," Yu Jae-Chul, a Seoul, South Korean priest said.
One South Korean student said he fears that war might break out at any time and that he might be called up as a reserve soldier.
The hostilities come six weeks after North Korea's President Kim Jong Il unveiled his youngest son as his heir-apparent and amid high tension over revelations the North has a new uranium enrichment facility.
"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," he said.
Meanwhile, North Korea's official news agency said the government will continue strikes if South Korea violates a disputed sea border.
South Korean President Lee Myung-bak responded in kind, warning his country would retaliate strongly if the North attacks again.