The United States is ready for combat against North Korea, the lead commander of the US Forces Korea has warned.
General Vincent K Brooks said it is important for the US and South Korea to maintain an "ironclad and razor sharp" alliance and be ready if talks between the two Koreas lead to a "negative outcome".
North Korean leader Kim Jong Un announced on New Year’s Day that the isolated country wants to join the Winter Olympics in South Korea’s Pyeongchang next month.
He called for an immediate dialogue with Seoul.
Gen Brooks, who leads the 28,500-strong joint US Forces Korea (USFK), told students at Seoul Cyber University he was pleased the talks were happening but his troops could not let their guard down.
"We can be generally pleased by the recent overtures that happened. But we must keep our expectations at the appropriate level," he said.
He said US and South Korean troops are trying to "stay steady while providing room for diplomacy and economic actions to take effect led by our national leaders".
General Brooks did not address Donald's Trump's exchange this week with Mr Kim, in which the US President boasted his "nuclear button" is bigger and more power than the North Korean leader's.
On Thursday Mr Trump and South Korean President Moon Jae-in agreed to delay their regular military drills during February's Winter Olympics, Korea's presidential office said.
On Wednesday the North and South reconnected their cross-border communication channel two years after it was shut down.
Gen Brooks called the move "sincere" but said it may be to keep South Korea, the US, China, Japan and Russia at loggerheads over the North so it could win "nuclear capable" status.
"We can’t ignore that reality," he said.
He compared North Korea to the centre of a hand's palm and the five regional powers as five fingers.
Mr Kim wants the five fingers to be separated but they should operate in "harmony and closely connected to one another" like a fist so there is enough pressure to change the dictator's course, he added.
He said President Trump and Mr Moon are his "two bosses" and he wants to leave room for them to be able to make the decisions to find a peaceful and democratic way to resolve the North Korea issue.
On Wednesday, it was revealed a North Korean ballistic missile crashed into one of its own cities, Tokchon, during a failed test in April.
A US government source told Asia-Pacific news website, The Diplomat, the missile’s engine failed one minute into the flight and it crashed down from an altitude of about 40 miles, causing considerable damage to industrial and agricultural buildings.
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Satellite imagery confirmed the missile’s landing spot.
North Korea fired 23 missiles during 16 tests in 2017, including three intercontinental ballistic missile (ICBM) tests.