The Netherlands has started legal action to free 30 crew members of Greenpeace's Arctic Sunrise - including two New Zealanders - charged by Russia with piracy after a protest against Arctic oil drilling.
"The Netherlands, as the state under whose flag the Arctic Sunrise sails, today started an arbitration process on the basis of the UN Convention of the Law of the Sea," Foreign Minister Frans Timmermans said in a letter in parliament.
The action is against what the Netherlands sees "as the unlawful detention of the ship (and) to have it released and its crew freed", Timmermans wrote.
Dutch Foreign Ministry spokesman Friso Wijnen said the Netherlands believed the crew's arrest was illegal as Russia should have first asked Dutch authorities' permission to board the ship.
Russian investigators have charged all Arctic Sunrise crew members with piracy, an offence that carries a prison sentence of up to 15 years.
A court in the northern city of Murmansk last week remanded the crew members in custody for two months, including freelance journalists, pending an investigation into their mid-September protest on an oil platform owned by energy giant Gazprom.
Timmermans wrote that if there was no progress in the next two weeks, the Netherlands could take their case to the International Tribunal for the Law of the Sea in Hamburg.
The UN-backed independent tribunal based in the northern German port city opened its doors in 1994, shortly after the UN's Convention on the Law of the Sea came into force.
It has the power to make rulings based on the convention, which spells out the law and rules governing the world's oceans, seas and its resources.
Russian investigators accused the activists of trying to seize property with threats of violence.
The Netherlands has previously called for the crew to be released, but also said that Russia has the right to try them.
Timmermans said in his letter that the Netherlands "continues to prefer a diplomatic solution".
Greenpeace denies the crew members - who come from 18 different countries including Australia, New Zealand, Britain, Russia, Canada and France - committed any crime.
A five-member arbitral tribunal will now be set up, and the Netherlands can ask for the immediate release of the ship and crew as a provisional measure, Greenpeace said.
In the September 18 protest several activists scaled the oil platform in the Barents Sea to denounce Russia's plans to drill in the Arctic.
Russian border guards then lowered themselves on to the Dutch-flagged Arctic Sunrise from a helicopter, locked up the crew and towed the ship to Murmansk, nearly 2000km north of Moscow. Meanwhile, the start of Dutch legal action will put added pressure on Australia to take action, said a local Greenpeace organiser.
Julien Vincent, who organised a Melbourne protest rally yesterday in support of the "Arctic 30" crew, said Greenpeace hoped that Prime Minister Tony Abbott and Foreign Affairs Minister Julie Bishop would raise the matter with Vladimir Putin and at Apec. "We're calling on any legal and diplomatic support we can get."
Around 140 protests organised by Greenpeace were held yesterday, including in Wellington.