Russia must compensate the Netherlands over the 2013 seizure of Greenpeace's Arctic Sunrise ship during a protest against Arctic oil drilling, an international court ruled on Monday.

The Permanent Court of Arbitration (PCA) "found that the Netherlands is entitled to compensation with interest for material damage to the Arctic Sunrise" and those who were onboard, the Hague-based body said in a statement.

Russian commandoes seized the Dutch-flagged ship in September 2013 and detained the 30 Greenpeace activists and journalists onboard after a protest at an offshore oil rig owned by Russian state oil giant Gazprom.

Moscow's angry response to the protest, during which two Greenpeace activists had tried to scale the drilling platform, sparked an international outcry.

The activists -- who became known as the "Arctic 30" -- were initially accused of piracy, a charge later changed to hooliganism, and detained for two months before being bailed and then benefiting from a Kremlin-backed amnesty.

Russia handed the ship itself back last year.

- 'Moscow breached obligations' -

In October 2013 the Netherlands hauled Moscow before the Hague-based PCA, a 117-nation body set up more than a century ago to arbitrate in disputes between countries, in protest at the seizure of the ship and its crew.

The Dutch asked the tribunal to rule that Russia had violated international maritime conventions.

It also asked for a ruling that Russia failed to comply with an order by the Hamburg-based International Tribunal for the Law of the Sea (ITLOS), which had ordered that Russia promptly release the ship and its crew.

Russia did not attend the Hamburg hearing, and did not take part in the PCA's arbitration either.

"Russia had failed to satisfy the 'promptness' of the requirements of the ITLOS," the PCA said in Monday's ruling.

This "amounted to a breach of Russia's obligations under the convention," it added.

Russia also has to pay back bail money raised by the Dutch to free the Arctic 30, the PCA said.

Findings made by the PCA are binding, but countries are entitled to ask, within a month, for a "correction" of an award -- when it believes a mistake was made when working out the costs of compensation, for instance.

- 'Right to demonstrate' -

Dutch Foreign Minister Bert Koenders hailed the PCA's decision, saying it gave a guarantee to any ship sailing in international waters that it "cannot just be summarily boarded or its crew arrested."

"Even if they (the crew) are using their right to demonstrate," Koenders added.

"Freedom of expression and the right to demonstrate are issues of great importance to the Netherlands which we'll defend."

Greenpeace also welcomed the ruling, saying it set an important precedent.

"We hope that this deters other countries from similarly aggressive attempts to stifle dissent, either on land or at sea," Greenpeace lawyer Daniel Simons said in a statement.

The latest PCA ruling is set to further cloud troubled Dutch-Russian relations in the wake of the MH17 air disaster last year.

The passenger jet was shot down over Ukraine in July 2014 during heavy fighting between government forces and pro-Russian separatists. All 298 people onboard -- the majority of them Dutch -- were killed.

Dutch investigators earlier this month said they had found fragments "probably" from a Russian-made surface-to-air missile at the crash site, but did not directly point the finger at Moscow.

Ukraine and many others in the West have accused the rebels of blowing the Boeing 777 out of the sky, saying they may have used a BUK missile supplied by Russia.

Moscow and the rebels deny any responsibility and blame Ukraine's military.