The two countries are set to begin their largest ever co-operative air exercise - dubbed Vigilant Ace - on Monday, with 230 aircraft, including F-22 Raptor stealth jet fighters, ready to take flight.
Part of the United States force taking part in the wargames, including a dozen of F-35B stealth jets, will fly from a Japanese airbase, where they have been stationed.
The maneuvers come as North Korea on Wednesday fired a new intercontinental ballistic missile (ICBM) which Seoul says is capable of flying some 13,000 kilometers, declaring that it has completed the "state nuclear force". Pyongyang lashed out at the drills as incitement to a nuclear war. In total, 230 aircraft will be flying at eight USA and South Korean military installations in the South.
"The Trump team is begging for nuclear war by staging an extremely risky nuclear gamble on the Korean peninsula", North Korea's Foreign Ministry stated in a statement on Saturday. The South Korea and US Air Forces hold annual Max Thunder exercises in the first half of the year and Vigilant Ace exercises in the second.
Dozens of people gathered outside the USA embassy in Seoul to protest against these biannual war games and demand all parties choose dialogue to resolve the current crisis peacefully, reports Efe news.
While denouncing Pyongyang's recent launch, Moscow has been accusing Washington of provoking North Korea with its saber-rattling in the peninsula.
South Korean media reports said B-1B Lancer bombers could join the exercise this week.
At the same time, various United States officials have been directing belligerent rhetoric at Pyongyang on nearly a daily basis.
Meanwhile, it was reported that South Korea army has launched a "decapitation unit" aimed at assassinating North Korea leader Kim Jong-un in case of war, The Korea Times reported.
North Korea has been eligible for even harsher sanctions since US President Donald Trump declared it a designated state sponsor of terrorism last month, and White House National Security Advisor H.R McMaster has admitted the newspaper editorial's warning of war was credible.