South Korea will host the Olympics in February amid rising tensions with North Korea.
Seoul and Washington usually hold their two annual military drills, called Key Resolve and Foal Eagle, in March and April, with some 17,000 American troops and more than 300,000 South Korean soldiers participating in the exercises.
Pyongyang is highly critical of those exercises, considering them preparations to invade the North. In response, it has been developing its weapons programs.
Earlier this month, North Korean state-run media described a joint exercise between the US and South Korea as a naval blockade against the North and warned that it would take "merciless self-defensive" measures.
The blockade, it added, would be a "wanton violation" of the country's sovereignty and dignity, and it accused the US president of taking an "extremely dangerous and big step towards the nuclear war" by seeking such an extreme measure.
South Korean President Moon Jae-in said on December 20 he was ready to postpone the joint military drill in order to reduce tensions with North Korea.
But Mattis said on Friday night that the United States will not change its military exercise schedule because of international concerns.
“The rescheduling of exercises will be, as always, subject to both countries,” Mattis told reporters. “If a pause is, I’m pausing them for a period of time because of a diplomatic issue or something, no, I don’t anticipate that right now.”
While North Korean leaders have denounced the joint military activity, which sometimes also involves Japan, as rehearsals for an invasion, the US and the South insist that the practices are defensive in nature.
Tensions between the two sides peaked earlier this month, when the US and its allies launched large-scale joint aerial drills in the Pacific, which involved more than 230 aircraft, including six F-22 Raptor stealth fighters.
The most recent exercise, dubbed the “Warrior Strike,” saw American and South Korean troops practice infiltrating North Korea and removing the country's nuclear weapons in the event of war, according to South Korea news agency Yonhap.
The war games were said to be a response to the North's test-firing of what US military experts said was an all-new Hwasong-15 missile capable of hitting targets across the US mainland.
‘Nothing impresses me’
Asked whether he was impressed by the North Korean gains, Mattis replied, “Nothing impresses me.”
Washington’s decades-long military presence in and around the Korean Peninsula has forced Pyongyang to develop its ballistic missiles and nuclear weapons as a deterrent against Washington's aggression.
North Korean leader Kim Jong-un has ordered the production of more rocket warheads and engines. Pyongyang says it will not give up on its nuclear deterrence unless Washington ends its hostile policy toward the country and dissolves the US-led UN command in South Korea. Thousands of US soldiers are stationed in South Korea and Japan.