The US deployed supersonic bombers and fighter jets in response to recent missile tests carried out by North Korea.
The B-1B bombers conducted joint aerial drills on Saturday with other South Korean and US warplanes, according to South Korea's joint chiefs of staff.
It said the drills demonstrated an "iron-clad" US security commitment to South Korea and the allies' combined defence posture.
North Korea drew widespread international condemnation on Friday after it test-launched an intercontinental ballistic missile (ICBM) capable of carrying multiple nuclear warheads and with a range that could reach anywhere on the US mainland.
North Korean leader Kim Jong Un watched the test with his daughter - the first time she had been seen in public - and boasted the ICBM was a "reliable and maximum-capacity" weapon to contain US military threats.
State media photos showed Mr Kim walking hand in hand with the girl, and together watching a huge missile loaded on a launch truck.
Friday's launch was part of the North's ongoing barrage of missile tests that are seen as an attempt to expand its weapons arsenal.
Some foreign experts said the Hwasong-17 missile is still under development, but is the North's longest-range ballistic weapon designed to carry multiple nuclear warheads to defeat US missile defence systems.
The North's Korean Central News Agency (KCNA) said the missile fired from Pyongyang International Airport travelled up to a maximum altitude of about 6,040km (3,750 miles) and flew a distance of about 1,000km (620 miles) before it landed in international waters off the country's east coast.
"The test-fire clearly proved the reliability of the new major strategic weapon system to be representative of (North Korea's) strategic forces and its powerful combat performance as the strongest strategic weapon in the world," KCNA said.
"Kim Jong Un solemnly declared that if the enemies continue to pose threats to [North Korea], frequently introducing nuclear strike means, our party and government will resolutely react to nukes with nuclear weapons and to total confrontation with all-out confrontation," KCNA said.
Mr Kim's statement suggests North Korea will continue its weapons testing activities as the US continues to bolster its security commitment to its allies South Korea and Japan.
There are concerns that, in coming weeks, North Korea could conduct its first nuclear test for five years.