Pyongyang. Hours after the United States deployed two nuclear-capable stealth bombers over South Korea as part of a "deterrence” mission over the Korean peninsula, North Korean leader Kim Jong-un ordered preparations for strategic rocket strikes on the US mainland and military bases.The order came as 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.”The deployment of B-2 bombers on Thursday followed North Korea’s decision to cut a military hotline with the South, breaking the last direct communication link between the two countries at a time of heightened military tensions.The bombers made the 20,000km round trip from the US state of Missouri to South Korea in a single flight. Clear message to North KoreaOn Wednesday, the North said it would inform the UN Security Council that the threat of nuclear war in the region is growing."Under the situation where a war may break out any moment, there is no need to keep up North-South military communications,” the official was quoted as saying by the official Korean Central News Agency. "From now, the North-South military communications will be cut off.”In response to the provocation, the US said it is ready to respond to "any contingency.”"North Korea’s bellicose rhetoric and the threats that they engage in follow a pattern designed to raise tensions and intimidate others,” Jay Carney, the White House spokesman, said. But Kim Jung-un, yesterday, directed his rocket units on standby at an overnight emergency meeting with top army commanders.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.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”.Meanwhile, 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”.While China, North Korea’s biggest trading partner, immediately reiterated its call for all sides to ease tensions.