Two daughters of one of the Japanese who hijacked a plane to North Korea are seeking to obtain Japanese nationality, sources close to the pair said Saturday.

A lawyer for the two daughters -- age 24 and 20 -- of the late Takeshi Okamoto asked the Tokyo Family Court on Thursday for an inquiry into their claims to citizenship, submitting to the court their birth certificates issued by a North Korean hospital, the sources said.

Of the 20 children born to the group of nine Japanese terrorists, only Okamoto's two daughters have not been granted Japanese nationality because their parents died soon after the hijacking.

Three daughters of three of the hijackers traveled from North Korea to Japan in May to settle permanently.

In March 1970, nine members of the Red Army Faction, a radical group known as "Sekigunha" in Japan, hijacked a Japan Airlines plane with 138 passengers and crew on board en route from Tokyo to Fukuoka and forced it to fly to Pyongyang.

Okamoto apparently married a Japanese woman after defecting to North Korea but his whereabouts were unknown from around 1982.

The other hijackers say Okamoto and his wife died in a landslide in 1988, but there have been reports that Okamoto may have been confined to a labor camp.

Okamoto is still on an international wanted list because his family has not reported his death to authorities.

Takeshi Okamoto is the elder brother of Kozo Okamoto, 53, a member of the Japanese Red Army terrorist team that staged the 1972 attack at Tel Aviv's Lod airport, now known as Ben Gurion airport, which left 25 people dead and 80 others injured.

Kozo Okamoto was given political asylum in Lebanon last year. The Japanese Red Army is a breakaway of the Red Army Faction.