North Korea removes missiles from launch site: US officials

North Korea has taken a major step back from a planned missile test, US officials said, even as Pyongyang and Seoul exchanged fresh threats today of swift military retaliation to any provocation.

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.

But the US defence official told AFP on condition of anonymity: "They moved them," and added that there was no longer an imminent threat of a test.

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.

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.

Although large-scale, annual joint drills were wrapped up at the end of last month, Pyongyang issued a fresh warning today over a smaller, joint anti-submarine exercise.

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.

In an interview with US broadcaster CBS ahead of her summit with Obama, President Park said any similar attack by the North would be met with a harsh military response."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.