Hundreds of US and South Korean warplanes participated in the combined military drills that began on Monday amid Seoul's sustained tensions with North Korea. The drills, one of the largest ever planned by the allies, will last for a week.
"South Korea and US Air Forces will work together with the joint services to perform major air missions such as close air support, defensive counter air, and emergency air operations 24 hours a day during the training period ... Support forces on the ground will also train their base defence procedures and survivability in case of attack," the US Air Force said in a statement.
More than 240 warplanes will conduct nearly 1,600 sorties during the drill, which has been code-named Vigilant Storm. The drill is in direct response to the increasing aggression of North Korea in recent weeks. There have been reports that North Korea is planning to launch a nuclear test, which will be its first such test since 2017.
The closer military cooperation between Seoul and Washington and more frequent joint drills come at a time when North Korean dictator Kim Jong-un has said Pyongyang's transformation into a nuclear power is irreversible. Analysts and geopolitical experts believe North Korea is close to achieving tactical nuclear weapons and that its plan is to nuclearise many of its new short-range missiles.
Meanwhile, North Korea said the US-South Korea drills are preparations for invasion. Pyongyang also launched missiles and fired artillery into the sea.
Earlier this month, the United States and South Korea fired missiles into the East Sea, in retaliation of the North Korean missile test a day earlier. The US and South Korea fired two short-range Army Tactical Missile Systems (ATACMS) each during the show. The combined forces also staged a bombing drill with fighter jets in the Yellow Sea.
The joint drill was conducted after North Korea fired a ballistic missile over Japan, prompting Tokyo to issue an alert asking residents to move to shelter. The ballistic missile passed over Japan and landed in the Pacific ocean after travelling 4,500 km.
Nuclear armed North Korea has been ratcheting up tension in the region for long, but this ICBM launch was the most daring act of provocation by Kim Jong-un in recent times. It was the first time in four years that Pyongyang is firing a missile over the territory of Japan.
In September, reports said an American nuclear-powered aircraft carrier was to is visit South Korea for combined drills with the South Korean navy. The US Forces Korea (USFK) said that the USS Ronald Reagan carrier strike group would conduct a routine port visit to South Korea.
Earlier this month, North Korean dictator Kim Jong-un said his military is capable of striking South Korea with nuclear weapons. The Pyongyang military is "completely ready to hit and destroy targets at any time from any location," Kim said.
"The effectiveness and practical combat capability of our nuclear combat force were fully demonstrated as it stands completely ready to hit and destroy targets at any time from any location .... Even though the enemy continues to talk about dialogue and negotiations, we do not have anything to talk about nor do we feel the need to do so," Kim said.