Neighbouring countries yesterday cautioned North Korea against carrying out a planned nuclear test, while a top South Korean security official said there was no sign a test was imminent.

China, Japan and South Korea all announced separate one-on-one summits among their leaders next week, increasing diplomacy over tensions caused by the North's announcement yesterday that it intended to conduct the test.

Such a test would confirm the North's claim that it has atomic weapon capabilities, and would severely undermine efforts to prevent an Asian nuclear arms race.

South Korea's top official on dealings with the North, Unification Minister Lee Jongseok, said there were no definite signs the test was imminent.

However, Lee also told politicians there was "a high possibility" it would eventually take place if "efforts to resume the six-party talks fail," Yonhap news agency reported.

North Korea has boycotted six-nation nuclear talks - which also involve China, Japan, Russia, South Korea and the US - for nearly a year, angered by US financial restrictions imposed over the North's alleged illegal activities such as money laundering and counterfeiting.

Meanwhile, an official at the North's embassy in Australia, Pak Myong-guk, who described himself as a minister, said Pyongyang's planned nuclear test "is not provocative".

"It is just the corresponding measure for defence, for us to defend ourselves," Pak said. "It is the really essential process for nuclear deterrent."

The North insists it needs the weapons to deter the US.

South Korea's President Roh Mooh-yun yesterday called for a "cool-headed and stern" response to the North's announcement, while Foreign Ministry spokesman Choo Kyu-ho said a nuclear test by North Korea could cause a change in its engagement policy toward the communist regime.

"If North Korea pushes ahead with a nuclear test, North Korea should take full responsibility for all consequences," Choo said after an emergency meeting of South Korean security ministers.

Asked to elaborate on what the consequences would be, Choo said a North Korean nuclear test could bring about a "shift" in Seoul's engagement policy toward the North, but also stressed that did not mean abandoning that policy altogether.

South Korea has consistently pursued dialogue with North Korea since their leaders first met in a historic summit in 2000. That approach has caused a rift with Washington.