The Netherlands has launched legal action to free 30 Greenpeace activists charged in Russia with piracy.
The group was arrested last month over a protest on an Arctic oil rig owned by state-controlled firm Gazprom.
Foreign Minister Frans Timmermans said he was also acting to free the Dutch-flagged Greenpeace ship Arctic Sunrise.
Greenpeace calls the charges against the activists, who include two Dutch citizens, "irrational, absurd and an outrage".
Mr Timmermans said the Netherlands had applied to the UN's Tribunal for the Law of the Sea, which resolves maritime disputes between states.
He said his country, the first nation to take legal action in the case, viewed the ship's detention as unlawful.
Under the rules of the Hamburg-based Tribunal, the Netherlands may apply for the immediate release of the ship and those on board.
"I really want to consult with my Russian colleagues... to get these people freed as soon as possible," Mr Timmermans said, according to Associated Press.
"I don't understand why this could be thought to have anything to do with piracy; I don't see how you could think of any legal grounds for that."
The BBC's Anne Holligan in The Hague says the dispute threatens to test the strong diplomatic ties between Russia and the Netherlands.
Citizens of 17 other countries, reported to include Britain, France, Canada and New Zealand, were also among those arrested and detained in the Russian city of Murmansk.
The group was seized during a skirmish with armed Russian security officers after several activists tried to board the Prirazlomnaya platform, Russia's first offshore oil rig in the Arctic.
They were later charged with "piracy of an organised group".
Greenpeace's international executive director, Kumi Naidoo, said earlier this week the charges were "extreme and disproportionate".
The Russian government has not commented on the Dutch legal action. President Vladimir Putin has said the environmental activists broke international law, although he has conceded they were not pirates.
Mikhail Fedotov, who heads the presidential council for human rights advisory body, said on Thursday he did not think there were "the slightest grounds" for a piracy charge.