Moscow has held three Ukrainian ships and 24 sailors since capturing them in the Kerch Strait in November.

Russia must release 24 sailors it arrested onboard three Ukrainian vessels last year as they crossed a strait between Russian-annexed Crimea and southern Russia, an international maritime tribunal said on Saturday.

The Russian navy captured the Ukrainian sailors and their vessels in the Kerch Strait, which links the Black and Azov seas, on November 25, 2018, after opening fire on them.

The Hamburg-based United Nation‘s International Tribunal for the Law of the Sea (ITLOS) said Russia had to release the sailors and vessels immediately.

“The Tribunal notes that any action affecting the immunity of warships is capable of causing serious harm to the dignity and sovereignty of a state and has the potential to undermine its national security,” ITLOS President Jin-Hyun Paik said.

Paik also said: “The tribunal considers it appropriate to order both parties to refrain from taking any action which might aggravate or extend the dispute.”

However, the tribunal “does not consider it necessary to require [Russia] to suspend criminal proceedings against the 24 detained Ukrainian servicemen and refrain from initiating new proceedings,” he added. Kiev had called for legal proceedings to be ended.

The sailors face up to six years in prison if found guilty.

Ukraine has already demanded the sailors’ release and the return of the impounded vessels, yet Moscow has not heeded the request or similar calls by the European Union.

Russia’s foreign ministry said on Saturday it had not participated in the hearings, adding it intends to defend its point of view that the arbitration lacked the jurisdiction to consider the Kerch incident.

Both countries signatories

The ITLOS was established to settle maritime disputes by the 1982 UN Convention on the Law of the Sea, of which both Ukraine and Russia are signatories. The tribunal’s decisions are legally binding, but it has no power to enforce them. The tribunal called for both sides to report back on their compliance by June 25.

Al Jazeera’s Dominic Kane, reporting from Hamburg, said that the ball is in Russian President Vladimir Putin‘s court as the tribunal has no means to enforce this judgment.

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“Does he want to listen to the judgment of the court, whose jurisdiction his country recognizes, or not?” he said.

A bilateral treaty gives both Russia and Ukraine the right to use the Sea of Azov, which lies between them and is linked by the narrow Kerch Strait to the Black Sea.

Russia, which annexed Crimea in 2014 and built a road bridge linking it to southern Russia straddling the Kerch Strait, has vowed never to give Crimea back to Ukraine. It accuses Kiev of staging a provocation in the Kerch Strait and its sailors of crossing illegally into Russian waters.

Russia’s FSB security service said it had been forced to act in November because the ships – two small Ukrainian armoured artillery vessels and a tug boat – had illegally entered its territorial waters.

“The Tribunal’s order is a clear signal to Russia that it cannot violate international law with impunity,” Ukraine Deputy Foreign Minister Olena Zerkal said on Facebook, adding she expected Russia to comply with the order quickly.

Ukrainian President Volodymyr Zelensky said if Russia releases the Ukrainian sailors and ships it could be the first signal from the Russian leadership of its readiness to end the conflict with Ukraine.