In a conversation with Japan's United Nations representative in New York, Pyongyang's UN representative said North Korea was not involved.

The two boats, which Tokyo says were spying, escaped after being fired on and pursued by Japanese ships and planes, and were reported by the Japanese to have docked in North Korea.

But North Korea's representative at the United Nations has told his Japanese counterpart that Pyongyang had no connection with the ships.

Japanese officials said the two ships entered a North Korean port, but added that they could not be positively identified as North Korean.

Unsucessful chase

The ships, first spotted by Japan's Maritime Safety Agency patrol boats, ignored orders to stop.

Prime Minister Keizo Obuchi held an emergency meeting of key cabinet officials and ordered the full participation of Japan's armed forces in the chase.

Keizo Obuchi held an emergency meeting

But the Japanese navy failed to catch the vessels. It was reported that the naval vessels ran out of fuel.

Correspondents described the chase as Japan's biggest military action since the World War II. The pursuit was called off when the boats reached international waters.

It was the first time a law allowing Japan's self-defence forces to take "necessary action in protecting human lives and assets, and maintaining security at sea" had been invoked.

The Japanese government called on North Korea to hand over the ships, which it said were masquerading as Japanese fishing boats, should they be found.

Fishing boat disguise

The unidentified boats were said to be about 30 metres long and 100 tonnes in weight, and "bristling" with antennae but with no fishing gear on board.

Chief Cabinet Secretary Hiromu Nonaka said the unidentified boats carried the names of genuine Japanese fishing vessels. He said one of the Japanese boats had been dismantled, and the other was operating in another area.

Later it was announced from the Pentagon in Washington that some US surveillance aircraft had supported the Japanese. "We obviously oppose the violation of territorial waters," spokesman Ken Bacon said.

New defence guidelines debated

By coincidence, the boat incident took place just as Japan is debating new defence guidelines.

Many opposition politicians are against the increased role that Japanese armed forces would have under the guidelines.

Prime Minister Obuchi, said that this kind of incident could happen again at any time and it was important for the government to be united in its response.

The incident came as Japan was hoping for a thaw in relations with North Korea.