North Korea has demanded that South Korea and the United States halt annual military drills due in February and March, saying they were a direct provocation, a statement that suggested a re-run of a sharp escalation in tension last year.
In 2013, North Korea said it would retaliate against any hostile moves by striking at the United States, Japan and South Korea, triggering a military buildup on the Korean peninsula and months of fiery rhetoric.
The reclusive North has regularly denounced annual drills such as "Key Resolve" and "Ulchi-Freedom-Guardian" staged by South Korea and United States as a prelude to invasion.
"We sternly warn the U.S. and the South Korean authorities to stop the dangerous military exercises which may push the situation on the peninsula and the north-south ties to a catastrophe," the North's KCNA state news quoted a body in charge of efforts to promote Korean unification as saying.
Similar bellicose rhetoric from the North set South Korea, the United States and Japan on edge a year ago. As a result, Washington flew Stealth bomber missions over South Korea and strengthened its military presence in the South, where nearly 30,000 U.S. troops are based.
South Korea said the drills were going ahead as planned and despite the threat, North Korea's military has showed no sign of unusual activities.
"If North Korea actually commits military aggression at the excuse of what is a normal exercise we conduct as preparation for emergency, our military will mercilessly and decisively punish them," Defence Ministry spokesman Kim Min-seok said.
North and South Korea remain technically at war after their 1950-53 civil conflict ended in a truce, not a treaty.
China, North Korea's only remaining real ally and which has been alarmed by what it sees as provocations by both sides, called for restraint.
"All sides have a responsibility to maintain peace and stability on the Korean peninsula and this accords with all sides' interests," Foreign Ministry spokesman Hong Lei told a daily news briefing.
"The overall situation on the Korean peninsula at present is quite fragile. We hope all sides can exercise restraint and not take steps to rile each other."
Analysts say the North cannot risk igniting a conventional military conflict it would almost certainly lose.
Many North Korea watchers believe the isolated country could instead launch another long-range rocket or push ahead with a nuclear test. It has conducted three nuclear tests, the last one in February last year.
The North could also stage another artillery attack on South Korean territory as it did in 2010, and risk provoking a military response from Seoul that could trigger a wider conflict.
The North's rocket launches are banned under United Nations resolutions because they are viewed as part of a process of proving the technology for an intercontinental nuclear weapon. Its nuclear program has also been sanctioned.
North Korean leader Kim Jong Un, who took power two years ago, has pursued his father's military policies, including those aimed at obtaining nuclear strike capacity.
(Reporting by David Chance; Additional reporting by Ben Blanchard in BEIJING; Editing by Nick Macfie)