North Korean leader Kim Jong-un (2nd R) looks at the latest combat and technical equipments, made by unit 1501 of the Korean People's Army, during his visit to the unit March 24, 2013 in this picture released by the North's official KCNA news agency in Pyongyang March 25, 2013. Reuters/KCNA
SEOUL (3RD UPDATE) - North Korean leader Kim Jong-Un on Friday ordered missile units to prepare to strike US mainland and military bases, vowing to "settle accounts" after US stealth bombers flew over South Korea.
The order came after US Defense Secretary Chuck Hagel, with tensions soaring on the Korean peninsula, said Washington would not be cowed by Pyongyang's bellicose threats and stood ready to respond to "any eventuality".
Kim directed his rocket units on standby at an overnight emergency meeting with top army commanders, hours after nuclear-capable US B-2 stealth bombers were deployed in ongoing US joint military drills with South Korea.
In the event of any "reckless" US provocation, North Korean forces should "mercilessly strike the US mainland... military bases in the Pacific, including Hawaii and Guam, and those in South Korea", he was quoted as saying by the official Korean Central News Agency (KCNA).
While North Korea has no proven ability to conduct such strikes, Kim said: "The time has come to settle accounts with the US imperialists."
The youthful leader argued that the stealth bomber flights went beyond a simple demonstration of force and amounted to a US "ultimatum that they will ignite a nuclear war at any cost".
A South Korean military official quoted by Yonhap news agency said a "sharp increase" in personnel and vehicle movement had been detected at the North's mid- and long-range missile sites.
The defence ministry declined to confirm the report, saying only that all strategic sites in the North were under intense South Korean and US surveillance.
The B-2 flights, which followed training runs by B-52 bombers, were part of annual drills between the United States and South Korea, which North Korea each year denounces as rehearsals for war.
Pyongyang has been particularly vocal this time, angered by UN sanctions imposed after its long-range rocket launch in December and the third nuclear test it carried out last month.
Kim's order formalised steps already taken by the Korean People's Army (KPA), which put its strategic rocket units at combat-ready status on Tuesday. The following day it cut the last remaining military hotline with South Korea.
China, North Korea's sole major ally and biggest trading partner, appealed for calm and said "joint efforts" were needed from all parties to prevent the situation deteriorating further.
The bulk of the threats emanating from Pyongyang have been dismissed as bluster. North Korea has no confirmed missile capability to reach the US mainland -- or indeed Guam or Hawaii in the Pacific.
But Washington has opted to match the threats with its own muscle-flexing.
"We will be prepared -- we have to be prepared -- to deal with any eventuality," Hagel told reporters at the Pentagon.
"We must make clear that these provocations by the North are taken by us very seriously and we'll respond to that," Hagel said.
US military intelligence has noted that the North's warlike rhetoric has not, so far, been matched by any overtly provocative troop build-up.
Present at the emergency meeting convened by Kim in Pyongyang were the KPA chief of general staff, director of operations and commander of strategic rocket operations.
KCNA provided an unusually precise timing for the meeting of 00:30 am (1530 GMT Thursday), in an apparent effort to underline the urgency and import of Kim's order.
But analysts warned against reading too much into what is the latest in a long series of incremental rhetorical upgrades.
"It shouldn't be taken to mean war is imminent," said Kim Yong-Hyun, a North Korea expert at Dongguk University.
"It's an inevitable and calibrated reaction to the B-2 deployment, and this who-blinks-first game with the United States will continue for a while yet," he said.
The North's official Uriminzokkiri website posted an animated propaganda video showing a North Korean missile shooting down a US B-52 bomber, which then crashes on South Korea with its nuclear payload detonating on impact.
"It's not a nuclear umbrella but nuclear rain that the US will pour down on the South," read an accompanying caption.
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