More than 17,000 American military personnel will join 50,000 South Koreans today in joint drills that North Korea warns will "pour gasoline on the fire" of tension in the region.
The two allies are set to begin 11 days of drills as South Korea's new military chief declared that the security conditions on the peninsula were "more serious than at any other time" as a result of Pyongyang's rapidly developing nuclear weapons programme.
Last month North Korea test-launched two ICBMs at highly lofted angles, and outside experts say those missiles can reach some USA parts like Alaska, Los Angeles or Chicago if fired at normal, flattened trajectories.
Moon said North Korea had not stopped its efforts to advance its nuclear and missile technologies, even as the global community strengthened pressure and sanctions on Pyongyang.
"They should not be seen in any way as a provocative exercise", Ms Payne said.
A confidential United Nations report, seen by Reuters on Monday, found North Korea evaded U.N. sanctions by "deliberately using indirect channels" to export banned commodities and had generated $270 million between October 2016 and May 2017.
Kang echoed the remark, saying that both military and diplomatic measures should go hand in hand, according to the South Korean Foreign Ministry.
"If the USA and South Korea carry out strikes and try to overthrow the North Korean regime and change the political pattern of the Korean Peninsula, China will prevent them from doing so".
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The actions include targeting major coal exporters that North Korea leader Kim Jong Un allegedly relies on to help fund his nuclear weapons and ballistic missile programs.
"The U.S. will be wholly held accountable for the catastrophic consequences to be entailed by such reckless aggressive war maneuvers, as it chose a military confrontation with the DPRK", read an English version of the statement, issued by an unidentified spokesman for the Korean People's Army mission at the truce village of Panmunjom and reported via the state-run Korean Central News Agency.
He said diplomacy was "the most important starting point" in response to the North's threat, when asked what actions by North Korea might trigger a preemptive US strike against it.
The top U.S. military commander in the Asia-Pacific region said Tuesday that the diplomatic approach is the "stronger and more powerful" means to resolve the standoff with North Korea, adding such efforts should be backed by credible military capability. North Korea, however, has long viewed the exercises as rehearsals for invasion.
The Security Council unanimously imposed new sanctions on North Korea on August 5 that could slash its $3 billion annual export revenue by a third.
"This right now is an exercise to make certain that we're ready to defend South Korea and our allies over there", Mattis told reporters aboard an aircraft flying to Amman, Jordan.
North Korea, for its part, threatened to launch missiles toward the American territory of Guam before its leader Kim Jong Un backed off saying he would first watch how Washington acts before going ahead with the missile launch plans.
It comes as the US and South Korea joined forces today to take part in an annual 10-day exercise, known as Ulchi-Freedom Guardian, involving tens of thousands of troops.