North Korea has criticised the arrival of the US aircraft carrier USS Nimitz in the South for a joint drill as an "extremely reckless" provocation and a rehearsal for war against the communist state.
A US naval strike group led by the nuclear-powered Nimitz arrived off the South's southern port of Busan Saturday for the drill to be staged this week, following joint exercises that infuriated North Korea in recent months.
The 97,000-ton Nimitz, one of the world's largest warships, will participate in joint search-and-rescue operations as well as "sea manoeuvring" around the Korean Peninsula, the South's defence ministry said.
The North's Committee for the Peaceful Reunification of Korea that handles cross-border affairs called the arrival of the US fleet "a grave military provocation" that would dramatically ratchet up tension.
"The joint naval drill involving the latest weaponry including the nuclear aircraft carrier is a wanton blackmail against us and demonstrates...that their attempt to invade us has reached an extremely reckless level," it said.
"The risk of a nuclear war in the peninsula has risen further due to the madcap nuclear war practice by the US and the South's enemy forces," the committee said in a statement carried by state-run KCNA Saturday night.
The latest joint naval drill between the two allies is expected to be staged off the South's eastern coast from Monday to Tuesday, Yonhap news agency reported, citing an unnamed Seoul official.
Military tensions on the Korean peninsula have been high for months, with the North under the young leader Kim Jong-Un issuing a series of apocalyptic threats over what it sees as intensely provocative US-South joint exercises.
The friction has abated somewhat after the annual ground exercises were wrapped up at the end of April, and a US defence official said North Korea had moved two medium-range missiles off their launch pads.
North Korean troops near the disputed Yellow Sea border have been ordered to strike back if "even a single shell drops" in their territorial waters, the North's army command said in a statement last week.
Any subsequent counterstrike would trigger an escalated military reaction that would see South Korea's border islands engulfed in a "sea of flames", it said.
The tense sea border off the west coast saw deadly naval clashes in 1999, 2002 and 2009. The North shelled one of the islands, Yeonpyeong, in November 2010, killing four South Koreans and sparking brief fears of a full-scale conflict.