The Netherlands has asked an international court to order Russia to release 30 people detained during a Greenpeace protest against oil drilling in the Arctic.
The Dutch government made the request at a tribunal that Russian officials refused to attend on Wednesday.
Liesbeth Lijnzaad, a representative of the Dutch government, said Russia had "violated the human rights" of the activists who tried to climb onto Russia's first offshore Arctic oil rig in September, detaining them for seven weeks "without grounds".
Russia has said it does not recognise the case, accusing the activists and their ship, the Dutch-registered Arctic Sunrise, of posing a security threat. Prosecutors charged the 30 people with piracy, but lessened the charge to hooliganism, which carries a maximum jail term of seven years.
The Russian president, Vladimir Putin, has said they are not pirates but has faced growing criticism over what is seen as Russia's heavy-handed treatment of the case.
"The dispute is worsening," Lijnzaad told the International Tribunal for the Law of the Sea in the German port of Hamburg.
Countries have no right to seize vessels belonging to third countries in their exclusive maritime economic zones, she said.
The Dutch hope the tribunal will rule by mid-November, securing the provisional release of the 30 activists who have been denied bail in a case that has strained relations between Russia and European countries, particularly the Netherlands.
A tribunal spokeswoman said no date had yet been set for a decision but that it could come around November 21.
Piracy charges remain
The court was established by the 1982 UN Convention on the Law of the Sea - of which both the Netherlands and Russia are signatories - to settle maritime disputes. Its decisions are binding but it has no means of enforcing them.
Nothing has changed despite the statement by Putin and from the investigative committee that the charges would be requalified to hooliganism
"We are very grateful to the Dutch government for bringing this case and to the tribunal for considering it," Greenpeace international general counsel Jasper Teulings said.
The global environmentalist group is based in Amsterdam.
"The argument of the Netherlands is that in international waters, ships have the right to freedom of navigation and so this means they may not be boarded, inspected, detained or arrested except with the permission of the flag state. There are exceptions to this, but they are limited," Teulings added.
Russia's Investigative Committee, which is handling the case, reduced initial charges of piracy to hooliganism in late October, cutting the maximum jail term from 15 years to seven.
Teulings, however, said that as far as Greenpeace was aware the 30 were now charged with piracy as well as hooliganism.
"Nothing has changed despite the statement by Putin and from the investigative committee that the charges would be requalified to hooliganism," Teulings said.
"As far as we are aware all 30 are still charged with both hooliganism and piracy."
The Russian prime minister, Dmitry Medvedev, last week reiterated Moscow's stance that Greenpeace posed a threat to the security of Russian workers and the environment by disturbing work at the platform.