A US defence official said two North Korean missiles -- primed for imminent test firing -- had been moved from their launch site, signalling a possible easing of North Asia tensions ahead of a US-South Korea summit in Washington.
US and South Korean officials had been worried that any test of the medium-range Musudan missiles would trigger a fresh surge in military tensions that have included threats of nuclear war from Pyongyang.
Pyongyang, which rattled the world with its third nuclear test in February, would have to make detectable preparations to return to a launch-ready status, two US officials said.
The move was revealed in Washington on the eve of a first summit between President Barack Obama and new South Korean President Park Geun-Hye at the White House today, intended as a strong signal of unity to Pyongyang.
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Tensions on the Korean peninsula have been on the brink of boiling over for months, with the North issuing a series of apocalyptic threats over what it sees as intensely provocative US-South Korean military exercises.
North Korean troops near the disputed Yellow Sea border with the South sector have been ordered to strike back if "even a single shell drops" in their territorial waters, the North's army command said in a statement.
Any subsequent counterstrike would trigger an escalated military reaction that would see South Korea's border islands engulfed in a "sea of flames," the statement added.
North Korea shelled one of the islands, Yeonpyeong, in November 2010, killing four South Koreans and sparking brief fears of a full-scale conflict.
"Yes, we will make them pay," Park said, adding that Seoul would no longer engage in a "vicious cycle" of automatically meeting the North's provocations and threats with negotiations and assistance.