North Korea has said it had placed its missiles on “standby" and warned it could strike American bases in South Korea and in the Pacific, in retaliation to the U.S. dispatching bombers to carry out flights over the Korean peninsula as part of a recent military drill.

While the North has in the past issued similar threats of attacking the U.S. and the South, Friday’s warning was seen by analysts as striking a note that was even more fiery than usual, heightening regional concerns.

The reclusive state’s young new leader Kim Jong-un, who took over following the death of his father Kim Jong-il in December 2011, had late on Thursday “signed the plan on technical preparations of strategic rockets of the Korean People’s Army" and had ordered them "to be on standby for fire so that they may strike any time the U.S. mainland, its military bases in the operational theaters in the Pacific, including Hawaii and Guam, and those in South Korea,” the official Korean Central News Agency (KCNA) said.

The announcement was met with concern not only across the border in Seoul, where officials said that they had observed heightened activity in some launch sites, but also in Beijing, where the North’s only ally – and biggest source of aid – called for all sides to bring down tensions.

“We call on all relevant parties to make joint efforts to turn around the tense situation,” Chinese Foreign Ministry spokesperson Hong Lei told reporters, using language that went beyond the usual Chinese response of calling for peace and stability in the Korean peninsula.

The North’s KCNA agency in another statement on Friday reminded the country’s neighbours that with the Armistice Agreement recently scrapped, “there is no mechanism to deter a war”.

“Upon hearing the statement of the Supreme Command of the Korean People’s Army, all service personnel and people are renewing their firm resolution to deal merciless and retaliatory blows at the vicious provocateurs and achieve a final victory in the war for national reunification,” the KCNA said.

It said the nullification of the agreement was “due to the grave provocations of the U.S. and the puppet group”, referring to the South, and added that “the Supreme Command of the Korean People's Army has already declared military actions against the U.S. mainland and the bases of the U.S. imperialist aggressor forces in Hawaii, Guam and the Pacific, to say nothing of the military targets and enemy ruling institutions in south Korea.”

Photographs issued by KCNA showed mass rallies in Pyongyang on Friday held to denounce the U.S., leading some analysts to suggest the North's moves were possibly aimed at shoring up domestic support for the new leader. The leadership's increasingly strong rhetoric has followed a rocket launch last year and a nuclear test in February that brought new sanctions, even as the country deals with a dire economy and food shortages.

How far the North will go as it continues to put forth dire warnings is unclear, analysts say, considering the state’s penchant for issuing similar threats in the past. In recent days following the flights of U.S. nuclear-capable stealth bombers over the Korean peninsula in a show of force along with the South, missile sites in the North have shown “increased activities”, the Seoul-based Yonhap news agency quoted military sources as saying.

The U.S. has indicated it will go ahead with planned drills with the South in spite of the threats, raising the prospect of further tensions in coming days. On Friday morning, the North dispatched a Mig-21 fighter close to the borders of the South’s front-line airspace, Yonhap reported. While the fight returned to base, the South responded by scrambling a fighter, officials said.

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