North Korea threatened a nuclear first strike Monday, as it railed against tougher international sanctions and the start of spring manoeuvres by the United States and South Korea.
In a statement through the state news agency, Pyongyang vowed a "pre-emptive and offensive nuclear strike" against the "undisguised nuclear war drills aimed to infringe upon the sovereignty" of North Korea.
Some 300,000 South Korean soldiers and 17,000 US troops are involved in the joint manoeuvres on the peninsula. The US has 28,500 soldiers stationed in South Korea.
The joint exercises beginning Monday "highlight the longstanding and enduring partnership and friendship between the two nations," the Combined Forces Command said.
North Korea said its "indiscriminate nuclear strike" would display the country's "military mettle."
North Korea issued similar threats three years ago ahead of the annual US-South Korean military exercises.
The manoeuvres come days after the UN Security Council imposed its strictest sanctions ever on Pyongyang, in response to the test of a nuclear device in January and a long-range rocket test last month.
The North Korean regime fired several short-range rockets off its eastern coast Thursday, hours after the sanctions vote in New York.
Monday's statement from Pyongyang said the "illegal and outrageous" sanctions make the country "boil like a crucible."
Seoul said Monday it would unveil new sanctions against North Korea amid the latest escalation of tensions.
The sanctions, to be announced Tuesday, are believed to include an entry ban on any ships that have been to North Korea, and adding more North Koreans to its blacklist, Yonhap News Agency said, citing unnamed sources at the prime minister's office.