North Korea hit out at Washington and Seoul Saturday, pledging to launch a blitzkrieg in the Korean peninsula, as the United States and South Korea launched their largest-ever joint landing drill.
The official KCNA news agency, citing a statement from military chiefs, warned of a "pre-emptive retaliatory strike at the enemy groups" involved in the joint US-South Korean exercise.
Pyongyang said it would respond to the drills with an "operation to liberate the whole of South Korea including Seoul" with an "ultra-precision blitzkrieg".
Responding to the statement, South Korea's defense ministry warned Pyongyang against further provocations, according to Yonhap news agency.
The new round of threats came as South Korea and the US launched the "Ssangyong" (twin dragons) landing drill.
The exercise involved 17,200 soldiers -- 12,200 US troops and 5,000 South Korean soldiers -- at the southeastern port of Pohang, a South Korean defense ministry spokesman said.
Later on Saturday, North Korean state media boasted of the nation's right to launch a "pre-emptive nuclear attack" and issued a final warning to Washington.
"A nuclear war against the DPRK would bring a final ruin to the US," read an article published in the North's Rodong Sinmun newspaper.
"This is the last warning of the DPRK to Obama and his cronies in the White House."
Meanwhile, news reports said a North Korean submarine had gone missing earlier this week, sparking a search by the North's navy.
The unknown class of vessel had been reportedly operating off the North Korean coast earlier in the week when it disappeared.
A South Korean defense ministry told AFP Seoul was investigating the reports, while Pentagon officials declined to comment.
The US military had been observing the submarine off the North's eastern coast, CNN said, citing three US officials familiar with the incident.
American spy satellites, aircraft and ships have been watching as the North Korean navy searched for the missing sub, the report added.
The United States is unsure if the missing vessel is adrift or whether it has sunk, CNN reported, but officials believe it suffered a failure during an exercise.
The US Naval Institute (USNI) News said the submarine was presumed sunk.
"The speculation is that it sank", an unidentified US official was quoted as telling the USNI News.
"The North Koreans have not made an attempt to indicate there is something wrong or that they require help or some type of assistance."
North Korea's navy operates a fleet of some 70 submarines, most of them rusting diesel submarines that are capable of little more than coastal defense and limited offensive capabilities.
But the old, low-tech submarines still pose substantial threats to South Korean vessels.