South Korea held live-fire military drills near its disputed Yellow Sea boundary with North Korea Monday, despite threats of retaliation.
The drills, which included artillery, mortars and helicopters, lasted about two hours.
North Korea warned it would respond to the drills with a "merciless" attack. However, South Korean officials have reported no immediate action taken by the North.
The North's threat appeared aimed at mustering internal support, or could be the result of top military officers showing their loyalty to Kim Jong Un, Yoo Ho-yeol, a professor at Korea University in South Korea told The Associated Press.
The communist country seems to focused on internal stability after the death of longtime dictator Kim Jong II. It will hold disarmament talks with the United States later this week.
U.S. military forces are also scheduled to conduct additional military exercises with South Korea over the next few months.
Leaders around the world are watching how North Korea's new leader Kim Jong Un, deals with the strained relationship with South Korea.
The Korean peninsula has been technically at war for about 60 years. The maritime line separating the countries was drawn by the U.S.-led U.N. Command without Pyongyang's consent at the close of the 1950-53 Korean War, which ended with a truce, not a peace treaty.
North Korea routinely argues that the line should run farther south.