Defence officials said the armed forces of both countries have been put on alert, although the South Koreans said they did not believe the missile test was imminent.

Japan's Kyodo news agency said warships were being sent to the Sea of Japan to monitor any new missile flight.

Kim Jong Il is thought likely to be named North Korean president imminently

Meanwhile, a South Korean government source said satellite and eavesdropping equipment by US forces and its own military "caught" North Korea readying for a second launch of the Taepo-Dong 1 missile, according to the Yonhap news agency.

Seoul officials said it was "impossible" to launch by Saturday, the day North Korean leader Kim Jong-Il is expected to be named president, because workers at the North Korean missile launch sites had not yet begun loading a missile with liquid fuel.

Food appeal

At the same time, North Korea has appealed for food and medical aid to cope with what is thought to be a worsening famine after bad weather destroyed crops.

North Korean missile launchers on parade in Pyongyang

The Japanese Government suspended shipments of food aid to North Korea in protest at the first test which flew over Japan on Monday and has said any repetition would be unacceptable.

The BBC Tokyo correspondent says Japan has been left feeling dangerously exposed, as it has no missile detection system of its own.

In response, the government has said it is considering setting up an intelligence satellite and possibly a missile defence system.

The official North Korean news agency, KCNA, said "Japan's behaviour is ridiculous, indeed, in view of the fact that Japan is zealously developing long-distance vehicles and other up-to-date weapons and paving the way for overseas aggression."

Referring to Japan's pre-World War II colonial past it said: "Japan must necessarily pay for the 40 odd years of its occupation of Korea and murder of Koreans and plunder."

Missile range

Japanese PM Keizo Obuchi has been urged to take strong action

The newly-developed North Korean missile has an estimated range of 1,500-2,000 kilometres, putting all the Japanese islands within reach.

The Japanese Government has warned North Korea that any further tests would be unacceptable and would upset moves towards normalising diplomatic ties.

"I want North Korean leaders to understand if they go ahead with an irretrievable thing, the way will be shut for another 50 years," said Chief Cabinet Secretary Hiromu Nonaka.

He criticised North Korea's statement on Wednesday in which North Korea said Japan was "making a fuss" about the test.

Mr Nonaka said Japan would "never allow tyranny" and has protested to the United Nations.

Japan's Upper House has also unanimously condemned the test, describing it as "a reckless and extremely dangerous act which took no heed of the possibility that it might land in our country's territory and completely ignores international common sense."