Greenpeace Japan has filed a legal complaint with the Tokyo District Court demanding that police return documents seized during an investigation into the environmentalist group's recent protest over dioxin pollution, members said.

The group called the seizure illegitimate and said the confiscated documents, which included lists of its members and supporters, are irrelevant to the case being investigated.

It also asked the court to nullify the police's confiscation record.

The documents were seized by police last Thursday during raids on Greenpeace International's flagship, the Rainbow Warrior, and Greenpeace Japan's Tokyo office.

The 555-ton Dutch-registered Rainbow Warrior was berthed in Tokyo as part of an Asian tour campaigning for a toxic-free Asia.

The ship's captain, Joel Stewart, from the United States, filed the complaint on behalf of the group.

The raid followed the May 9 arrests of four Greenpeace International members for trespassing after they scaled a tower near an incinerator in Tokyo's Toshima Ward and unfurled a giant banner proclaiming Tokyo the world's "dioxin capital."

The group said police seized the ship's logbook and leaflets and copied a computer file containing a membership list.

Greenpeace Japan did not deny trespassing, but took issue with the seizure of membership documents. "Pictures were taken of the entire event and Greenpeace admitted the activity," Greenpeace Japan said in a statement.

"The seizure of the membership list is an invasion of the right to privacy and the right to organize, all guaranteed under the Japanese Constitution."

The four being detained are Al Baker from Britain, Marleen van Poeck from Belgium, Hong Kong-born Canadian Clement Lam and Paul Schot from the Netherlands.

The group said the act was to protest "Japan's reckless waste-incineration policy," which they contend is producing large quantities of dioxin.

Tests have found that burning waste can produce dioxins, which are toxic chemicals believed to cause cancer and fetus deformities.