North Korea has test-fired three short-range missiles, fuelling tension sparked by its nuclear standoff, as a US team held talks in China on ways to make UN sanctions bite against Pyongyang.

The projectiles were thought to be ground-to-ship missiles and were launched in the early evening on Thursday into the East Sea (Sea of Japan), South Korea's defence ministry said.

It was the first military action which the hardline communist state had taken since the United Nations on June 12 imposed tougher sanctions for its May 25 nuclear test.

The North had warned Japanese ship operators on Wednesday to stay clear of some areas off its east and west coasts during military exercises lasting until July 11, raising the spectre of more tests in the near future.

South Korea's JoongAng Ilbo newspaper, quoting an intelligence source, said the North in the coming days is likely to fire a series of short-range missiles.

Apart from ground-to-ship weapons with a range of 140 kilometres, it said these would likely include Scud-B missiles with a range of 340km.

The North may also fire Rodongs, whose 1,300km range would likely be shortened to some 400km for the current round of testing, the paper predicted.

In the days after its atomic test - the second since 2006 - Pyongyang had fired a total of six short-range missiles and renounced the truce in force on the Korean peninsula.

In response to the UN resolution tightening curbs on its missile and atomic activities it had vowed to build more nuclear bombs.

US and South Korean officials believe ailing leader Kim Jong-Il, 67, is staging a show of strength to bolster his authority as he tries to put in place a succession plan involving his youngest son.

Japan's prime minister Taro Aso condemned the exercise, telling reporters: "We have repeatedly warned that such a provocative act is not beneficial for North Korea's national interest."

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