The four also plan to ask for return from North Korea of two Japanese women who are married to two of the hijackers, Yukio Yamanaka, head of a Tokyo human rights group helping the hijackers, told reporters.

The four -- Takahiro Konishi, Shiro Akagi, Kimihiro Uomoto, Moriaki Wakabayashi -- plan to lodge the request with Prime Minister Yukio Hatoyama as early as April, Yamanaka said.

Of the original nine hijackers, three are believed to have died, while one was arrested in Japan in May 1988 after sneaking into the country using an illegally obtained passport and another was arrested by Thai authorities and turned over to Japanese police in March 2000.

Japan has long demanded that North Korea extradite the remaining four.

The four have filed similar requests with prime ministers when the Liberal Democratic Party ruled Japan almost uninterruptedly after the end of World War II.

Yamanaka said they filed a fresh request because Hatoyama's Democratic Party of Japan took power last year and also because this year marks the 40th anniversary of the so-called Yodo-go incident, in which the nine hijacked JAL Flight 351 while it was on a domestic flight from Tokyo to Fukuoka on March 31, 1970.

In what was the first hijacking in Japan, the hijackers took 129 passengers and cabin crew hostage and forced the pilot to fly to Pyongyang where they were granted political asylum.

Yamanaka said the four hijackers in North Korea are willing to return to Japan with the two wives to undergo trial, but they first want Uomoto and the wives to be taken off an international wanted list for their alleged involvement in North Korea's abduction of Japanese nationals in the 1970s and 1980s.

They are willing to cooperate with investigations into the matter in the meantime, he said.