U.S. Navy units participating in the exercise include USS Stethem (DDG 63), USS Ronald Reagan (CVN 76), and USS Mustin (DDG 89). Pyongyang stated that any act of aggression by the USA and South Korea would only "advance their own demise".
The deployment of US strategic military assets to South Korea came amid the heightened tensions on the Korean Peninsula following the Democratic People's Republic of Korea's (DPRK) sixth nuclear test in September.
A second South Korean official who spoke anonymously said USA forces are "irregularly" being deployed to the peninsula to participate in drills and joint training, and without disclosing deployment ahead of time, according to Yonhap.
Pyongyang responded to the report through its state-run KCNA news agency, which said, "If the U.S. imperialists and the South Korean puppets ignite an aggressive nuclear war against us, it would only advance their own demise".
South Korea will field a Sejong the Great-class destroyer, P-3 Orion anti-submarine aircraft, F-15k, FA-18 and A-10 fighter jets, as well as Lynx and AW-159 Wild Cat naval choppers.
The exercise will provide a visible and coordinated engagement for the U.S. - ROK alliance.
A US nuclear-powered submarine on Friday made a port call at a city in southeast South Korea, Yonhap news agency reported Friday.
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Washington has in recent days attempted to ramp up pressure on Pyongyang by deploying strategic military assets to the Korean peninsula.
The vessel is carrying Tomahawk cruise missiles, used by the U.S.in the early April attack on Syria's Shayrat airbase.
The smaller USS Tucson, which is capable of firing Tomahawk cruise missiles, made a port call last Saturday at the USA base in Chinhae.
The U.S. Navy said the submarine is capable of "supporting Special Operation Forces (SOF) missions" and providing "unprecedented strike and special operation mission capabilities from a stealthy, clandestine platform".
"Measuring more than 360 feet long, Tucson is one of the stealthiest and most advanced submarines in the world", the navy said in a written statement.
The U.S. aircraft trained in the East Sea, also known as the Sea of Japan, where they conducted "virtual air-to-air missile fire drills", according to Seoul's joint chiefs of staff.