An international arbitration panel says Russia must compensate the Netherlands for seizing a Greenpeace ship protesting at an oil platform in Arctic waters in breach of an international treaty regulating the laws of the sea.

The Arctic Sunrise, sailing under a Dutch flag, was seized by Russian authorities in September 2013 during a protest against an offshore oil platform, and the 30 people on board were arrested and detained in Russian prisons for months.

They were eventually released shortly before the Sochi Olympics.

The Permanent Court of Arbitration announced the ruling Monday. It said the amount of compensation to be paid by Russia will be decided at a later date. Russia did not take part in the arbitration.