The US and South Korea have begun one of their largest ever joint-military aerial exercises.
Some 230 aircraft - including two dozen stealth jet fighters – have landed in South Korea ahead of the drills.
North Korea has warned the manoeuvres represent an "open, all-out provocation."
The drills are scheduled to last five days and come less than a week after the rogue state's latest intercontinental ballistic missile test, which Pyongyang claimed was capable of hitting the US mainland.
Codenamed, ‘Vigilant Ace,’ the exercises are meant to improve the allies' wartime capabilities and preparedness, South Korea's defence ministry said.
The US Seventh Air Force has sent six F-22 and 18 F-35 stealth fighter jets among hundreds of other aircraft. Around 12,000 military personnel are taking part.
In an editorial on Sunday, North Korea's ruling party Rodong newspaper said the US-South Korea drill "may lead to a nuclear war at any moment."
The piece - which came shortly after leader Kim Jong Un visited a military tyre factory - added: "The US and South Korean puppet warmongers would be well advised to bear in mind that their DPRK-targeted military drill will be as foolish as an act precipitating their self-destruction."
Mr Kim's factory trip saw him thank workers who had built the tyres for the huge vehicle used to transport the tested Hwasong-15 missile last week, which had prompted a public rally and fireworks in Pyongyang as the country continued to flout international sanctions.
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 HR McMaster has admitted the newspaper editorial's warning of war was credible.
"I think it's increasing every day, which means that we are in a race to be able to solve this problem," he said at a forum on Saturday.
"There are ways to address this problem short of armed conflict, but it is a race because he's getting closer and closer, and there's not much time left."
Meanwhile, the US agency tasked with protecting America from missile attacks is reportedly scouting the West Coast for places to deploy new anti-missile defences.
Two congressmen have claimed the defences would likely include Terminal High Altitude Area Defence (THAAD) anti-ballistic missiles, similar to those deployed in South Korea to protect against a potential North Korean attack.