North Korea has threatened "indiscriminate" nuclear strikes against South Korea and the US if the two allies go ahead with joint military drills on Monday.
The announcement, described as a "pre-emptive nuclear strike of justice", was made in a statement by the Supreme Command of the Korean People's Army on Sunday, AFP reports.
More than 300,000 South Korean and 15,000 US troops will take part in the drill, understood to be their largest ever joint military exercise, Yonhap news agency reports.
The exercises, which begin on Monday and will last until 30 April, are intended to caution North Korea against nuclear incitements, South Koran defence minister Han Min-koo is reported as saying.
The drills will begin days after the United Nations Security Council passed the toughest sanctions in two decades against North Korea after it carried out a nuclear bomb test and launched a long-range missile, causing security tensions to increase.
North Korea has responded by saying it was preparing nuclear weapons and firing short-range nuclear weapons into the sea.
On Thursday, hours after the UN’s decision, the country fired six short-range projectiles into the sea off its east coast, South Korean officials said.
North Korean leader Kim Jong-Un has ordered the country's nuclear arsenal to be placed on standby for use "at any moment".
Military analysts, however, have cast doubt over the country’s ability to put nuclear warheads on its missiles, according to the BBC.
The US and South Korea opened talks on Friday over the deployment of the US missile defence system to counter the growing threat from North Korea – a move fiercely opposed by North Korea, Russia and China, according to AFP.