Greenpeace activists have gathered to mark 25 years since the sinking of the Rainbow Warrior, their iconic flagship, and to hold a keel-laying ceremony to start construction of a new Rainbow Warrior ship.

Leaders from the environmental group, including Kumi Naidoo, the executive director, and Peter Willcox, captain of the original Rainbow Warrior, which was sunk by French secret agents in 1985, assembled in Gdansk, Poland on Saturday.

The new vessel, which is expected to be completed in October 2011, will rely mostly on sail power.

The environmental group says the third-generation Rainbow Warrior will help them with campaignsto defend forests and protect oceans, while showcasing green-technology.

Nuclear protest

French agents bombed the original ship while it was docked in New Zealand in order to prevent Greenpeace activists from staging protests against French nuclear tests in the Pacific Ocean.

The attack, launched with underwater mines shortly before midnight on July 10 1985, killed Fernando Pereira, 35, a Portuguese-Dutch crewman and photographer and severely damaged French political credibility in the region.

Two French agents posing as tourists were arrested by New Zealand police after the 1985 bombing, although the police believed other conspirators got away.

The agents pleaded guilty to manslaughter and were sentenced to 10 years in jail.

UN settlement

France used trade pressure to push New Zealand into accepting a United Nations brokered settlement in 1986, which transferred the agents to what was supposed to be three years of exile in French Polynesia.

The agents were home in France by 1988, outraging some New Zealanders and Pacific islanders.

The first Rainbow Warrior, whose names come from a North American Indigenous prophecy, was a converted fisheries research trawler built in 1955.

The sunken boat was replaced in 1989 by another fishing vessel, Rainbow Warrior 2. That ship, now 52 years old, is due to be retired.