A Russian court on Sunday ordered the detention for two months of eight more crew members of a Greenpeace ship who protested against Arctic oil drilling as part of a probe into alleged piracy.

The Lenin district court in the northern city of Murmansk on Thursday had already ordered the detention of 22 other Greenpeace activists for two months, pending the investigation into suspected piracy after a protest at a Gazprom oil rig on September 18.

With the court's decision on Sunday, all 30 members of the Arctic Sunrise icebreaker crew will remain in custody until November 24.

Among their total are six British citizens, four Russians and nationals from 16 other countries including Argentina, Italy, France and Australia.

Reacting to the news of the detentions, Kumi Naidoo, executive director of Greenpeace International, said in a statement that the court's decision was a "blatant attempt to intimidate anyone preventing an oil rush in the Arctic".

Diplomats from several countries attended the hearings.

Russian investigators have accused the activists of piracy after two tried to scale state energy giant Gazprom's Prirazlomnaya oil platform in the Barents Sea.

The group has denied committing piracy and accuses Russia of illegally boarding its ship in international waters.

President Vladimir Putin has said that the activists "are of course not pirates" but stressed they had broken international law by getting dangerously close to the oil rig.

Charges of piracy carry a maximum prison term of 15 years but the Investigative Committee said the charge against the group could be reduced in the course of the probe.

'I am not a pirate'

Those detained include Dmitri Litvinov, a Greenpeace spokesman and a Swedish-American dual citizen of Russian origin, Sini Saarela, a Finnish activist who tried to scale the platform, and Frank Hewetson of Britain.

According to a Greenpeace statement, Saarela said at the beginning of his hearing on Sunday: "I am an honest person and I always answer for my actions. I'm not a pirate."

Also among those detained was the vessel's captain, Peter Willcox, who was also the skipper of Greenpeace's Rainbow Warrior ship, which French secret services bombed and sank in New Zealand in 1985.

Another is photographer Denis Sinyakov, a former staff photographer at AFP and Reuters who was working for Greenpeace as a freelancer.

The Dutch government called on Moscow to release the activists immediately and said it was considering legal action.

The arrests also sparked outrage from Russian and international rights activists, with Reporters Without Borders saying investigators were "criminalising both journalists and environmental activists".

Fourteen of those detained are being held in a pre-trial detention centre in Murmansk, while others have been transferred to the nearby city of Apatity.

In an apparent violation of a law stipulating that foreign suspects should be held separately from Russian nationals, a British activist is being held with two Russians suspected of robbery, said Irina Paikacheva, the head of a state-connected regional prisoner rights watchdog.

"That is a violation," she told AFP.

Other activists are likely to get cellmates from ex-Soviet countries because keeping suspects by themselves would also contravene the law.

Paikacheva noted that according to Russian law, the Greenpeace crew cannot be held together because they have all been detained on the same charges.

One of those detained suffers from asthma, she added.

Overall, they are being held in "satisfactory conditions", Paikacheva said. "The food is decent. The cells are rather spacious."

The detention centres where suspects are held before trial in Russia are called Investigative Isolators and do not differ much from common Russian jails notorious for their filthy conditions and prisoner abuse.