By Katie Stallard, Russia Correspondent
Representatives of the Dutch government have appealed to an international maritime court to try to secure the release of the Arctic Sunrise and its crew.
The Greenpeace ship, which was sailing under the Netherlands flag, was seized by Russian security forces in September after a protest near an arctic oil rig.
Thirty people on board, including two freelance journalists, a cook and the ship's doctor were arrested at gunpoint and taken to a pre-trial detention centre in Murmansk.
Last week, without explanation, they were transferred to a prison in St Petersburg.
Initial charges of piracy have reportedly been downgraded to hooliganism, an offence punishable by up to seven years in prison. But Greenpeace said the original charges also remain in place.
Russian security services seize Arctic SunriseThe Dutch government has applied to the International Tribunal for the Law of the Sea to order the immediate release of the ship and its crew.
Based in Hamburg, the tribunal was set up to resolve global maritime disputes.
Russia had already said it would not take part in the hearing, and does not accept decisions that concern its national sovereignty.
The tribunal's website says its has no means to enforce its decisions.
But Greenpeace legal counsel Daniel Simons told Sky News the Netherlands had a very strong case, and it would be more appropriate for Russia to contest the issue of jurisdiction in court.
He said: "Russia has failed to indicate any legal basis for the boarding and detention of the vessel and those persons on board.
"So I think there's every prospect the tribunal will order their release, pending the arbitration case that the Netherlands has filed against Russia."
The Netherlands insists the ship was in international waters when it was stormed.
Inside the detention centre in MurmanskRussia has said it was in its exclusive economic zone, endangered a Russian oil platform, and should be subject to Russian laws.
Relations between the two countries have been strained since the incident.
The Netherlands and Russia celebrate 400 years of cultural ties this year.
That is not quite going according to plan.
Two weeks after the Arctic Sunrise was seized, a Russian diplomat was arrested and, he has claimed, treated roughly by police in The Hague.
Ten days later, a senior Dutch diplomat was assaulted in his Moscow flat.
Now Russian public health officials are investigating concerns about the safety of imported Dutch tulips and cheese.
Dutch Foreign Minister Frans Timmermans told reporters ahead of the hearing: "The Netherlands is hoping now that all this, eventually, will mean that pending a final solution of the issues, the crew will be released and that also the ship is going to be released."
"Our interpretation of the law of the sea is that nothing happened which justifies the crew being in prison.
"The judge must now decide."