But Satoru Miyamoto, a researcher at the Japan Institute of International Affairs, said: "At this stage, it is impossible for Japan to independently deter North Korean moves.

"Japan needs to show to the North that it is in a coalition with the United States," he said.

North Korea in 1998 fired an earlier version of the missile over Japan into the Pacific Ocean, leading Washington and Tokyo to race to develop missile defenses.

But this time Japan would have added fears as North Korea has since declared itself a nuclear power. Negotiations on the nuclear standoff have been at a standstill since late last year.

"You never know what is loaded in the warhead of a missile fired by North Korea," Miyamoto said. "It could be a nuclear bomb.

"Even if it is just one nuclear missile, Japan needs to take measures to stop the North from launching a missile, no matter what," he said.

"Japan needs to show, if they fire a nuclear missile, there would be retaliation and they would also be attacked by nuclear arms," said Miyamoto, an expert on security in the Far East.

Japan is believed to be capable of quickly becoming a nuclear power but analysts said it was unrealistic for Tokyo to go nuclear considering the financial and political costs.

As the only country to have been attacked with nuclear weapons, Japan has campaigned for their abolition, while coming under the US nuclear umbrella.

"There remains a powerful allergy among the Japanese people against nuclear weapons," said Masayuki Masuda, a research fellow at the National Institute for Defense Studies.

Japan was forced to renounce the means of war after defeat in World War II. Since then its troops, called the Self-Defense Forces, have not fired a single shot on battlefields despite a more than 40 billion-dollar budget this year.

Neighboring countries haunted by Japan's past aggression have been quick to condemn any move away its official pacifism.

"In the current legal framework under the pacifist constitution, Japan's Self-Defense Forces can move only after Japan is attacked," Masuda said. "So amid the current North Korean activities, there's nothing the SDF can do."

The only unilateral option, he said, would be economic sanctions, which Japan has already threatened. It also threatened them in a separate row over the North's kidnappings of Japanese civilians in the 1970s and 1980s.

A study by Japan's ruling Liberal Democratic Party said last year that sanctions would badly hit the North's fragile economy by cutting off remittances from Koreans in Japan and banning Pyongyang's ships.

But Miyamoto doubted that Japanese sanctions would have as much impact as the government says.

"Economic sanctions would do nothing as there is almost no trade between North Korea and Japan," he said. "No matter how much Japan accuses the North of human rights violations, it wouldn't affect a country that is not even a member of the international community."

Lee Yeong-Hwa, a Korean resident in Japan and an expert on North Korea at Kansai University, said Tokyo should focus on better monitoring Pyongyang.

Japan relies heavily on US intelligence and only plans to send off its own spy planes in the current fiscal year to March 2008.

"What Japan needs is not nuclear arms but better intelligence capability," Lee said.

Japan calls for diplomacy to stop NKorean missile

Japan called Wednesday for diplomacy to persuade North Korea to drop reported plans for a missile launch.

"It's important that nations cooperate and persuade North Korea to cancel the launch," Chief Cabinet Secretary Shinzo Abe, the government spokesman, said to reporters.

He was responding to news that former South Korean president and Nobel laureate Kim Dae-Jung had put off a trip to Pyongyang amid concern that the North would test-fire a long-range Taepodong-2 missile

North Korea on Wednesday called for talks with the United States on its missile launch plans.

A series of reports have said North Korea was preparing to test-fire a Taepodong-2 missile with a range of up to 6,700 kilometres (4,200 miles), far enough to hit targets in Alaska and possibly Hawaii.

North Korea fired a Taepodong-1 over northern Japan into the Pacific in 1998, raising international concern and leading Japan and the United States to develop a missile defense system.

Japanese foreign ministry press secretary Yoshinori Katori downplayed the possibility that Japan would have to use missile defense.

"If North Korea test-launches, it is likely to fall into the ocean, somewhere in international waters," he said. "I don't want to speculate on the possibility of using missile defense at this point."

US ambassador to Japan Thomas Schieffer said earlier the United States was keeping "all options on the table" to stop a missile.

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