BBC wrote:Russia has warned of tensions in North Korea slipping out of control, after Pyongyang said it was placing its missile units on stand-by.
Russian Foreign Minister Sergei Lavrov warned the situation could slip "toward the spiral of a vicious circle".
Kim Jong-un made the missile order after talks responding to US stealth bomber flights over the Korean peninsula, state news agency KCNA said.
The time had come to "settle accounts" with the US, KCNA quoted him as saying.
Annual military drills and fresh UN sanctions have angered North Korea.
After a late-night meeting with the army's strategic rocket force, Kim Jong-un "judged the time has come to settle accounts with the US imperialists", KCNA reported.
He was said to have condemned US B-2 bomber sorties over South Korea as a "reckless phase" that represented an "ultimatum that they will ignite a nuclear war at any cost on the Korean Peninsula".
US mainland and bases in Hawaii, Guam and South Korea were all named as potential targets.
The US - which flew two stealth bombers over the peninsula on Thursday as part of the ongoing annual US-South Korea military drills - has said it is ready for "any eventuality" on the peninsula.
CNN wrote: North Korea's leader approved a plan to prepare standby rockets to hit U.S. targets, state media said Friday, after American stealth bombers carried out a practice mission over South Korea.
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.
The rockets are aimed at U.S. targets, including military bases in the Pacific and in South Korea, it said.
"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.
Reuters wrote:KCNA said North Korea and the United States could only settle their differences by "physical means". The North has an arsenal of Soviet-era short-range Scud missiles that can hit South Korea but its longer-range Nodong and Musudan missiles, which could in theory hit U.S. Pacific bases, are untested.
China, the North's sole major ally, repeated its calls for restraint on the Korean peninsula at a regular Foreign Ministry briefing and made no criticism of the U.S. flights.
"We hope that relevant parties will work together in pushing for a turnaround of the tense situation," ministry spokesman Hong Lei told reporters.
Tension has been high since North Korea conducted a third nuclear weapons test in February in breach of U.N. sanctions and despite warnings from China for it not to do so.
Russia's foreign minister implicitly criticised the U.S. bomber flights.
"We are concerned that alongside the adequate, collective reaction of the U.N. Security Council, unilateral action is being taken around North Korea that is increasing military activity," Foreign Minister Sergei Lavrov said.
Not looking too good if they don't back down.
