"As two peace-loving nations, the Republic of Korea and America welcome the Olympic Games talks between the ROK and DPRK while at the same time remaining steadfast with the international economic pressure campaign to denuclearise the Korean peninsula," Mattis said in Honolulu.
The defence secretary was speaking at the start of a meeting with his South Korean counterpart Song Young-Moo at US Pacific Command, or PACOM, headquarters.
"Diplomacy should repose reason on Kim's reckless rhetoric and dangerous provocations," Mattis said, warning that the Winter Olympics talks and the respite in inter-Korean ties that accompany them do not solve overarching problems.
Pyongyang has agreed to send athletes and support delegations to the South for the Winter Olympics in Pyeongchang next month and form a unified women's ice hockey team with the South.
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The move followed months of entreaties from Seoul to take part in a "peace Olympics," prompting a rare and rapid improvement in the atmosphere on the peninsula.
But the North is also preparing a massive military parade in Pyongyang on February 8, a day before the Winter Olympics' opening ceremony.