According to the report, North Korea used the Russian Federation ports of Nakhodka and Kholmsk to transport coal on at least three occasions previous year after the UNSC banned exports of coal and other items with the August 5 passage of Resolution 2371.
"Instead, we have maintained close coordination in order to completely address North Korea's nuclear weapons through South Korea-US combined capability and intelligence capability among South Korea, US and Japan".
"Our response to this threat remains diplomacy led, backed up with military options available to ensure that our diplomats are understood to be speaking from a position of strength", the secretary explained. "We could fight tonight, shoulder to shoulder with the South Koreans, if they're attacked", the defense secretary told reporters en route from Vietnam to Hawaii.
Mattis also praised South Korea for recent efforts to enforce North Korean violations of United Nations economic sanctions, but stressed that diplomacy, backed by military power, must be the focus of the US effort to achieve stability on the Korean Peninsula.
Any North Korean attack would be "severely rebuffed", Mattis added.
Washington agreed to delay them until after the Olympics, which will be held on February 9-25 in the South Korean alpine town of Pyeongchang. "It's an worldwide problem that requires an global solution".
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If such plans are finalized, it would mark the first direct South Korean flight to the North since former first lady Lee Hee-ho made a rare goodwill visit to Pyongyang in 2015, the official said.
North Korea has violated the United Nations sanctions by shipping coal to Russian Federation three times.
US and South Korean military officials insist the war games, which involve tens of thousands of troops, are defensive in nature and necessary to maintain a constant state of readiness.
Regarding the possibility that South Korea could arm itself with nuclear weapons, the minister said the government will stick to the principle of denuclearization made in 1992 when the two Koreas pledged to abandon all nuclear weapons deployed on the Korean Peninsula, including United States tactical nukes. He has also at various times suggested he is willing to meet with North Korean leader Kim Jong Un. "The global pressure campaign [against North Korea] must continue", Mattis declared, adding that "our aim remains a complete and verifiable and irreversible de-nuclearization (CVID) of the Korean Peninsula".
A senior South Korean administration official said the planned exercises add urgency to efforts to use the current conciliatory mood to bring all sides to the table.
He thanked US allies in the region for their support in upholding ongoing sanctions against North Korean products that have been ratcheted up in response to a slew of missile tests in 2017.