The Netherlands said Friday it has started legal action to free 30 crew members of Greenpeace\'s Arctic Sunrise, 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. Russian investigators said on Thursday they have charged all Arctic Sunrise crew members with piracy, an offence that carries a prison sentence of up to 15 years in Russia. A court in the northern city of Murmansk last week remanded in custody for the months the crew members, including freelance journalists, pending an investigation into their protest on an oil platform owned by energy giant Gazprom last month. Timmermans wrote that if there was no progress in the next two weeks, the Netherlands could take their case to the Hamburg-based International Tribunal for the Law of the Sea, which makes rulings relating to the convention. 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 Britain, Russia, New Zealand, Canada and France -- committed any crime. \"Russian officials will now be called to explain their actions before an international court of law, where they will be unable to justify these absurd piracy allegations,\" Greenpeace International’s General Counsel Jasper Teulings said in a statement sent to AFP. 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. The September 18 protest saw several activists scale the oil platform in the Barents Sea to denounce Russia\'s plans to drill in the Arctic. Russian border guards then lowered themselves onto the Dutch-flagged Arctic Sunrise from a helicopter, locked up the crew and towed the ship to Murmansk located nearly 2,000 kilometres north of Moscow. \"While we hope that the Russian prosecutor and courts come to the same conclusion well before these international proceedings are concluded, and the defendants are released, the Dutch legal action sends a strong political signal and gives us hope that justice will prevail,\" Teulings said. President Vladimir Putin has said that in his opinion the activists were not pirates but had breached international law by getting dangerously close to the oil rig. Campaign groups including Human Rights Watch have called for their release. The unusually tough charges for a protest has sparked comparisons with the case of the Pussy Riot punks who were last year sentenced to two years in a penal colony for demonstrating against Putin in a Moscow church. A prisoners\' rights activist told AFP this week that the Greenpeace detainees were complaining of cold cells, chain-smoking fellow prisoners and difficulties communicating with guards, hardly any of whom speak English. Greenpeace held a similar protest at the same oil platform last year without incurring any punishment.