SEOUL, Feb. 4 (Yonhap) -- South Korea and the United States on Monday began a joint naval drill along the eastern coast, military officials said, sending what appears to be a warning to North Korea as it threatens to conduct a third nuclear test.
The three-day exercise kicked off earlier in the day in the East Sea to test the combat readiness of the two allies, in an apparent effort to give a warning to North Korea ahead of its possible nuclear test in the northeastern tip of the country.
Two U.S. ships equipped with long-range cruise missiles -- the USS San Francisco, a 6,800-ton nuclear submarine, and the 9,800-ton Aegis cruiser Shilo -- were mobilized for the exercise held near the eastern port city of Pohang.
The South Korean Navy deployed 10 vessels, including one 7,600-ton Aegis destroyer, a corvette and its newest Type-214 submarines as well as anti-submarine and maritime surveillance aircrafts and maritime helicopters.
"Naval forces of South Korea and the United States started to carry out drills in the East Sea," an official at the Joint Chiefs of Staff said. "The exercise involves naval maneuvers, submarine detection, live-fire drills and anti-ballistic missile drills."
Gen. Jung Seung-jo, the JCS Chairman, last Friday said the joint drill aims to guard against possible North Korean provocations involving submarines.
North Korea has a large fleet of submarines, and one of them is suspected to have torpedoed a South Korean Navy warship in the Yellow Sea in March 2010 killing 46 sailors.
The latest move comes after Pyongyang has threatened to carry out its third nuclear test in response to United Nations Security Council sanctions imposed for its December long-range rocket launch.
On Sunday, the North's state media said Kim Jong-un made an "important" decision regarding the communist state's security and sovereignty, fueling expectations for an imminent nuclear test.
South Korean and American intelligence officials have been analyzing daily updates from satellite imagery of the Punggye-ri site, where one of three tunnels has been recently covered with a camouflage net in an attempt to foil their efforts to detect early signs of a nuclear test.
Earthquake monitoring stations and military officials have been on standby to detect seismic tremors and measure increased radiation in the air in case of a detonation.