Story highlights A North Korean photo shows Kim Jong Un meeting with military officials

North Korean media: Rockets should be ready to "mercilessly strike" the U.S.

A Pentagon spokesman urges North Korea to "dial down the temperature"

"No one wants there to be war on the Korean Peninsula," he says

North Korea's leader has approved a plan to prepare rockets to be on standby for firing at U.S. targets, including the U.S. mainland and military bases in the Pacific and in South Korea, state media reported.

In a meeting with military leaders early Friday, Kim Jong Un "said he has judged the time has come to settle accounts with the U.S. imperialists in view of the prevailing situation," the state-run KCNA news agency reported.

"If they make a reckless provocation with huge strategic forces, [we] should mercilessly strike the U.S. mainland, their stronghold, their military bases in the operational theaters in the Pacific, including Hawaii and Guam, and those in South Korea," KCNA reported.

Later Friday, North Korean state media carried a photo of Kim meeting with military officials. The young leader is seated in the image, leafing through documents with four uniformed officers standing around him.

On the wall behind them, a map entitled "Plan for the strategic forces to target mainland U.S." appears to show straight lines stretching across to the Pacific to points on the continental United States.

South Korea and the United States are "monitoring any movements of North Korea's short, middle and middle-to-long range missiles," South Korean Defense Ministry Spokesman Kim Min-seok said Friday.

Kim's regime has unleashed a torrent of threats in the past few weeks, and U.S. officials have said they're concerned about the recent rhetoric.

"North Korea is not a paper tiger, so it wouldn't be smart to dismiss its provocative behavior as pure bluster," a U.S. official said Wednesday.

Photos: Photos: Militaries and Korean tensions Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – Emergency service personnel wearing chemical protective clothing participate in an anti-chemical warfare exercise on Tuesday, April 16 in Seoul. Tensions remain high in the Korean Peninsula in the wake of North Korea's recent nuclear threats and provocations. A Pentagon intelligence assessment suggests the North may have the ability to deliver a nuclear weapon with a ballistic missile, though the reliability is believed to be "low." Hide Caption 1 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – South Korean marines arrive on the island of Yeonpyeong near the disputed waters of the Yellow Sea on Friday, April 12. Hide Caption 2 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – A Japanese soldier is on alert as Patriot Advanced Capability-3 missile launchers are deployed at the Defense Ministry in Tokyo on Wednesday, April 10. Hide Caption 3 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – South Korean soldiers sit in a truck at the Inter-Korean transit office on Tuesday, April 9, in Paju, South Korea. Hide Caption 4 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – South Korean soldiers participate in an artillery drill as part of the Foal Eagle joint military exercise by U.S. and South Korean forces near the Demilitarized Zone in Goseong on April 9. Hide Caption 5 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – U.S. soldiers are at a military training field in Yeoncheon, South Korea, on April 9. Hide Caption 6 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – South Korean soldiers with K-55 self-propelled Howitzers stage at a military training field in the border city of Paju on Friday, April 5, as tensions continue to mount on the Korean peninsula. Hide Caption 7 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – South Korean soldiers man a cannon at a military training field in Paju on April 5. Hide Caption 8 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – South Korean soldiers stand guard at a sentry post at the border with North Korea in the Demilitarized Zone near Imjingak, South Korea, on April 5. Hide Caption 9 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – A U.S. Army Patriot missile battery is visible at the U.S. Osan Air Base in South Korea on Friday, April 5. Hide Caption 10 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – The U.S. Navy is moving a sea-based radar platform, like the one seen in this 2006 file photo, closer to the North Korean coast to monitor that country's military moves, including possible new missile launches, a Defense Department official said Monday, April 1. Hide Caption 11 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – South Korean marines man K-55 self-propelled Howitzers at a military training field in the border city of Paju on Monday, April 1. Park Geun-hye, South Korea's new president, promised a strong military response to any North Korean provocation after North Korea announced that the two countries were in a state of war. Hide Caption 12 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – South Korean anti-aircraft armored vehicles move across a temporary bridge during a river crossing drill in Hwacheon near the North Korean border on Monday, April 1. Hide Caption 13 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – South Korean soldiers ride on a military truck in Paju on Friday, March 29. Hide Caption 14 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – The United States said Thursday, March 28, that it flew stealth bombers over South Korea to participate in annual military exercises amid spiking tensions with North Korea. Pictured, a B-2 Spirit stealth bomber flies over South Korea's western port city of Pyeongtaek. Hide Caption 15 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – South Korean soldiers gather at the foot of a mountain near a military drill field in the border city of Paju on Wednesday, March 27. Hide Caption 16 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – Armed South Korean soldiers walk on a road near a military drill field in Paju on March 27. Hide Caption 17 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – South Korean soldiers ride in a military truck in Paju on March 27. Hide Caption 18 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – A B-52 bomber flies over the wire-topped fence of a U.S. air base in Osan, South Korea, on Tuesday, March 19. Hide Caption 19 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – South Korean soldiers take part in a drill to guard the building of a state-run telecom company in Seoul against potential guerrilla attacks on Thursday, March 14. Hide Caption 20 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – South Korean army soldiers jump off a military truck during a drill outside a U.S. airbase in Pyeongtaek as part of annual joint exercises with the United States on March 14. Hide Caption 21 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – South Korean Marines operate K-55 self-propelled howitzers on the western island of Ganghwa near the disputed maritime frontier with North Korea on Wednesday, March 13. Hide Caption 22 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – South Korean soldiers stand guard as a North Korean soldier, far center, looks on at the truce village of Panmunjom in the demilitarized zone dividing the two Koreas on March 13. Hide Caption 23 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – South Korean marines patrol on the South Korea-controlled island of Yeonpyeong near the disputed waters of the Yellow Sea on Tuesday, March 12. Hide Caption 24 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – In this Navy handout image taken on March 5, Lt. j.g. Matthew Harmon serves as helm safety officer aboard the guided-missile destroyer USS McCampbell during a replenishment at sea, part of Foal Eagle 2013, the joint exercises between the United States and South Korea. Hide Caption 25 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – Fire Controlman 2nd Class Jason Titcombe, left, hands Fire Controlman 2nd Class Joshua Clements ordnance aboard the destroyer USS Lassen in this Navy handout photo taken on March 5. Hide Caption 26 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – U.S. Navy Boatswain's Mate 3rd Class Brittany Chiles signals to an SH-60B Seahawk helicopter as it lands on the flight deck of the destroyer USS McCampbell on March 4 in the Pacific Ocean, in this Navy handout photo. Hide Caption 27 of 28 Photos: Photos: Militaries and Korean tensions Militaries and Korean tensions – This March 17 Navy handout image shows the destroyer USS John S. McCain, front; the Republic of Korea Navy destroyer ROKS Seoae-Yu-Seong-Ryong, center; and the destroyer USS McCampbell moving into formation in the waters off the Korean Peninsula during exercise Foal Eagle 2013. 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But Pentagon spokesman George Little said Thursday that it was important to remain calm and urged North Korea to "dial the temperature down."

"No one wants there to be war on the Korean Peninsula, let me make that very clear," he told CNN's "Erin Burnett Outfront."

Behind North Korea's heated words about missile strikes, one analyst said, there might not be much mettle.

"The fact is that despite the bombast, and unless there has been a miraculous turnaround among North Korea's strategic forces, there is little to no chance that it could successfully land a missile on Guam, Hawaii or anywhere else outside the Korean Peninsula that U.S. forces may be stationed," James Hardy, Asia-Pacific editor of IHS Jane's Defense Weekly, wrote in an opinion column published Thursday on CNN.com

North Korea's latest threat Friday morning came after the United States said Thursday that it flew stealth bombers over South Korea in annual military exercises

The mission by the B-2 Spirit bombers, which can carry conventional and nuclear weapons, "demonstrates the United States' ability to conduct long-range, precision strikes quickly and at will," a statement from U.S. Forces Korea said.

The North Korean state news agency described the mission as "an ultimatum that they (the United States) will ignite a nuclear war at any cost on the Korean Peninsula."

The North has repeatedly claimed that the exercises are tantamount to threats of nuclear war against it.

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But the U.S. military stressed that the bombers flew in exercises to preserve peace in the region.

"The United States is steadfast in its alliance commitment to the defense of the Republic of Korea, to deterring aggression, and to ensuring peace and stability in the region," the statement from U.S. Forces Korea said, using South Korea's official name. "The B-2 bomber is an important element of America's enduring and robust extended deterrence capability in the Asia-Pacific region."

The disclosure of the B-2 flights comes a day after North Korea said it was cutting a key military hotline with South Korea , provoking fresh expressions of concern from U.S. officials about Pyongyang's recent rhetoric.

Tensions escalated on the Korean Peninsula after the North carried out a long-range rocket launch in December and an underground nuclear test last month, prompting the U.N. Security Council to step up sanctions on the secretive regime.

Pyongyang has expressed fury over the sanctions and the annual U.S.-South Korean military exercises, due to continue until the end of April.

The deteriorating relations have put paid to any hopes of reviving multilateral talks over North Korea's nuclear program for the foreseeable future. Indeed, Pyongyang has declared that the subject is no longer up for discussion.

While Kim appears to have spurned the prospect of dialog with U.S. and South Korean officials, he met with Dennis Rodman during the U.S. basketball star's bizarre recent visit to North Korea.

Sharp increases in tensions on the Korean Peninsula have taken place during the drills in previous years. The last time the North cut off military communications with the South was during similar exercises in March 2009.

North Korea has gone through cycles of "provocative behavior" for decades, Little said Thursday.

"And we have to deal with them. We have to be sober, calm, cool, collected about these periods. That's what we're doing right now," he said. "And we are assuring our South Korean allies day to day that we stand with them in the face of these provocations."

The recent saber-rattling from Pyongyang has included threats of pre-emptive nuclear strikes against the United States and South Korea, as well as the declaration that the armistice that stopped the Korean War in 1953 is null and void.

On Tuesday, the North said it planned to place military units tasked with targeting U.S. bases under combat-ready status.

Most observers say North Korea is still years away from having the technology to deliver a nuclear warhead on a missile, but it does have plenty of conventional military firepower, including medium-range ballistic missiles that can carry high explosives for hundreds of miles.

Little said Thursday that the United States was keeping a close eye on North Korea's missile capabilities.

"The important thing is for us to stay out ahead of what we think the North Korean threat is, especially from their missile program," he said. "They've been testing more missiles, and they've been growing their capabilities and we have to stay out ahead."