French spy agent Jean-Luc Kister has broken his silence over the 1985 bombing of Greenpeace boat Rainbow Warrior, telling France's Mediapart and TVNZ's Sunday programme that now is the right time to speak up about the death of photographer Fernando Pereira.

The French agent who planted the bombs that sank the Rainbow Warrior has apologised for his actions.

More than 30 years after the attack on the Greenpeace vessel, which killed photographer Fernando Pereira and shocked the nation, the man who lead the combat dive team, Colonel Jean-Luc Kister, has broken his silence.

He told TVNZ's Sunday programme that the operation was a "a big, big failure" and it has weighed on his conscience ever since.

GREENPEACE The Rainbow Warrior lies half-submerged in Auckland Harbour after a bombing by French secret service agents in this 1985 photograph.

"For us it was just like using boxing gloves in order to crush a mosquito. It was a disproportionate operation, but we had to obey the order, we were soldiers," he said.

"Many times I think about these things because, for me, I have an innocent death on my hands."

Kister, who lives in Metz in northern France, said he wanted to apologise to the family of Pereira, to Greenpeace and to the people of New Zealand for what he did.

TVNZ Colonel Jean-Luc Kister says he is sorry for his part in the bombing of the Rainbow Warrior.

He was working for France's spy agency, the DGSE, when he placed two bombs on the Rainbow Warrior while it was docked in Auckland on its way to protest against French nuclear testing at Mururoa Atoll, near Tahiti, in 1985.

The attack was carried out just before midnight on July 10. The time was chosen because it was thought no one would be in the engine room, Kister said.

"We are not cold-blooded killers. We did everything to preserve the lives of the people on board the Rainbow Warrior."

GREENPEACE Photographer Fernando Pereira who was killed during the bombing of the Rainbow Warrior.

The two bombs were timed to go off about four minutes apart. The French agents believed the first explosion would scare any crew members off the ship while the second would sink it.

But the first bomb blew a 2m by 2m hole in the Rainbow Warrior's hull, near the engine room, sinking it much faster than the French expected, Kister said.

The second bomb, on the ship's keel, ended up killing Pereira.

Kister said he was surprised when asked to carry out an attack on the Rainbow Warrior, but the justification given was that Greenpeace had been infiltrated by Russian KGB spies.

He denied any suggestion that it was a terrorist attack. "For us, it was a sabotage operation and nothing more."

Two of the 13 agents who took part - Alain Mafart and Dominique Prieur - were arrested by New Zealand police two days after the bombing.

They were charged with murder and eventually received 10-year jail terms after pleading guilty to manslaughter, but they were freed within months.

Charles Hernu, the French Minister of Defence at the time, initially denied his country's involvement. But he was forced to resign months later after French newspaper Le Monde revealed a third team of French combat divers had been involved.