North Korea has placed its military on alert and warned of "disastrous consequences" in response to a United States-led military drill near the Korean peninsula.
A North Korean military spokesman Tuesday told state media all troops have been ordered to "keep themselves ready to promptly launch operations at any time."
South Korean Defense Ministry spokesman Kim Min-seok confirmed North Korea's military has been placed on high alert.
"Our armed forces are closely monitoring the North Korean military's movements and are fully prepared to take a decisive action against the North's possible provocations."
The threat comes as the U.S. moved a group of ships to the South Korean port of Busan for what officials describe as a routine search and rescue drill.
Pyongyang seems to be particularly upset about the participation of the USS George Washington, a nuclear-powered aircraft carrier.
The article in the Korean Central News Agency (KCNA) claimed the ship was carrying "at least 100 nuclear bombs aboard."
It warned the closer that U.S. forces get to North Korea, "the more unpredictable disasters their actions will cause."
Pyongyang often threatens military action in response to the U.S.-South Korean drills, but rarely follows through.
Leonid Petrov, a Korea analyst at the Australian National University, tells VOA he views the threats as part of a "seasonal type" of escalation.
"Every time the United States' and the Republic of Korea's naval or aerial exercises take place on the southern side of the peninsula, the North Koreans take it very seriously."
Petrov says North Korea views the drills as preparation to invade, a sentiment he says reflects the ongoing tension surrounding the Korean War.
"The Korean War is technically still going on, and every time the military on one side or the other is beefing up its forward deployed military, the other side reacts and sometimes overreacts."
The North's war-like rhetoric reached a peak not seen in years following international condemnation of its nuclear test in February. At its worst point, North Korea was issuing near-daily threats of nuclear war against the U.S. and its regional allies.
Relations had recently shown signs of improvement, with the two Koreas reaching tentative agreements on resuming a series of cross-border projects, including a symbolic joint factory that had served as a bellwether of Korean ties.
But the KCNA article warned that "the situation on the Korean peninsula is getting strained again." It said this is "entirely attributable" to what it called the "persistent anti-DPRK military confrontation of the U.S. and Japanese aggressors and South Korean puppet forces."
The South's Yonhap news agency the start of the three-day exercise, which involves U.S., South Korean and Japanese troops, has been delayed for a day because of bad weather.