TOKYO (AFP) - A senior Japanese defence official Saturday urged "crisis-management measures" ahead of a possible nuclear test by North Korea after its humiliating failure to launch a rocket.

The launch was supposed to be the centrepiece of weekend commemorations marking the centenary of the birth of North Korean founding leader Kim Il-Sung, and helping to formalise a new cult of personality around Kim Jong-Un.

But the rocket flew for just over two minutes before it broke up and fell into the Yellow Sea, with the North admitting a satellite had failed to enter orbit.

"We'd better keep in mind that they may conduct a nuclear test," Senior Vice Minister of Defence Shu Watanabe told a weekly news programme on the private TV Tokyo network.

"We must prepare crisis-management measures by remembering that they will surely do something in order to restore their damaged dignity," he said, amid fears that Pyongyang will hold another nuclear test.

Analysts say satellite imagery showing what looks like preparations, and the communist regime's previous patterns of behaviour -- with missile tests followed by bomb tests -- suggest a third nuclear test could be imminent.

North Korea has said its rocket launch was a peaceful attempt to put a satellite into orbit but the United States, South Korea and Japan have condemned it as a poorly disguised ballistic missile test.

Watanabe said countries should not have high hopes for change under Kim Jong-un, who inherited the regime from his father Kim Jong-Il, who died in December.

"We'd better not have hopes for the man, Kim Jong-un," the vice minister said.

"The man is just a beginner of brinksmanship diplomacy. The cronies from the Kim Jong-Il era choreograph him. The country will continue to be a source of global instability even after its leaders changed," he said.

 "What we should fear is that they may go ahead with missile and nuclear tests again even though the technologies are inadequate," he said.