North Korea has threatened to unleash a pre-emotive nuclear attack on the US and South Korea if they do not halt a joint annual military exercise.
The National Defense Commission of North Korea issued a statement saying the joint exercises pose a direct threat to the country, calling it an "undisguised nuclear war drill."
"As the joint military exercises to be staged by the enemies are regarded as the most undisguised nuclear war drills aimed to infringe upon the sovereignty of the DPRK, its military counteraction will be more preemptive and offensive nuclear strike to cope with them," the statement published by the KCNA news agency said.
Earlier last week, North Korean leader Kim Jong Un had ordered the military to be ready to use nuclear weapons any time, following the UN sanctions on the country for its pursuit of nuclear weapons and missile technology.
The joint military exercise between South Korea and the US is the largest ever this year, with around 17,000 American troops and about 300,000 South Korean soldiers taking part.
The drill focuses on the so-called "decapitation operations" against Pyongyang regime and pre-emptive strikes on its nuclear and missile facilities, the Chosun Ilbo newspaper reported.
The annual military drill by the allies is a conventional season of belligerent stance from Pyongyang but this time the posturing involves unmasked threats of nuclear strike.
Among the vessels featuring in the war games is the nuclear-powered aircraft carrier USS John C. Stennis, which can carry more than 80 aircraft including FA-18 E/F Super Hornet fighter jets.
The United Nations Security Council unanimously adopted last week a resolution that vastly expands sanctions on North Korea after its nuclear and missile tests.
Under the tough new sanctions North Korean ships suspected of carrying illegal goods will be banned from ports across the world, while 16 new individuals and 12 organisations from North Korea have been blacklisted.
The sanctions are the strongest imposed by the Security Council in more than 20 years.
The sanctions were imposed following a rocket launch by Pyongyang earlier this month, which had come after a nuclear test in January.