On Monday, the annual springtime joint exercises kicked off in South Korea. The US contingent includes some 17,000 troops, which is said to be the largest number of US forces in South Korea in decades. Washington has stepped up efforts at deploying strategic weaponry in South Korea in response to North Korean violations of UN resolutions, specifically its nuclear test and ballistic missile launch earlier this year.
"The focus of the exercises will be on hitting North Korea's key facilities precisely," one of the officials told Yonhap News Agency.
Another source said that the allies had an operational plan under which they would be practicing hypothetical attacks on North Korea's leadership and its nuclear arsenal, in the event of a war on the Korean Peninsula. The plan also stipulates training operations to detect, destroy and defend against North Korea's alleged nuclear weapon and missiles.
North Korea sees the joint exercises as a pretext for war and a direct threat to Pyongyang, and promised on Monday to launch a nuclear strike "of justice" in the event that the enemy "even slightly" threatens North Korea.
Last week, North Korean leader Kim Jong Un put his country on nuclear high alert, so its nuclear weapons may be used at any moment.
During last year's Seoul-Washington exercises, Pyongyang fired short-range ballistic and surface-to-air missiles as it believed the drills to be part of an invasion of the North.