US Defense Secretary Jim Mattis has said that the decision to delay joint military exercises with South Korea until after the Winter Olympics was made for practical reasons, rather than as a political gesture. "For us, it's a practical matter," Mattis told reporters, noting that the Olympics are South Korea's biggest event in terms of international tourism. "We have at times changed the timelines on these (drills) for any number of reasons, so for us, this is the normal give and take that we have," he added. He added that the drills would be conducted sometime after the Paralympics, which end on March 18. After a year that saw tensions on the Korean peninsula spike to their worst levels in years, 2018 has begun on a tentatively warmer note with Seoul responding positively to North Korean leader Kim Jong-Un's New Year speech. On Wednesday, the two Koreas restored a cross-border hotline that had been shut down since 2016. They also agreed to hold high-level talks next week - the first since 2015 - which will focus on "matters of mutual interest," including the North's participation in the Winter Olympics. Mattis said the talks were the result of international pressure, pointing to successive United Nations Security Council votes against the North. "It shows again that the democracies and the nations that are trying to keep this from going to war and stopping the provocations of nuclear weapon development, of ballistic missile launches and that sort of thing are united in trying keep this thing in a diplomatic-solution vein," he said. The Pentagon chief declined to address a recent tweet from President Donald Trump, who said Washington had a nuclear button that was "much bigger and more powerful" than North Korean leader Kim Jong-Un's. "My job as the secretary of defense is to make certain that we have forces ready to defend this country," Mattis said.