An international tribunal on Saturday urged Russia to release "immediately" 24 Ukrainian sailors seized last November off the Crimea peninsula.
"The Russian Federation must proceed immediately to release the Ukrainian soldiers and allow them to return to the Ukraine," said Judge Jin-Hyun Paik at the International Tribunal for the Law of the Sea, which is located in the German port city of Hamburg.
The tribunal judges additionally ruled Russia should "immediately" return the three Ukrainian navy vessels -- Berdyansk, Yani Kapu and Nikopol -- it seized in the Kerch Strait off Crimea, which Moscow annexed in 2014.
Ukraine took the matter to the tribunal last month -- but Russia does not recognise its jurisdiction to rule in the affair and did not send representatives to the hearing.
"The continued denial of freedom to the Ukrainian sailors is worrying from a humanitarian point of view," said Paik, heading a tribunal tasked with overseeing maritime disputes since 1982 and which 168 states recognise, Russia included.
- 'Clear signal' -
"The tribunal ruling is a clear signal to Russia that it cannot violate international law with impunity," Ukraine's vice minister for foreign affairs Olena Zerkal said on her Facebook page after the judgement.
New Ukraine President Volodymyr Zelensky wrote on Facebook that if Russia complies with the tribunal's demand to release the sailors then that "could be the first signal from the Russian leadership about real readiness to end the conflict with Ukraine."
Former President Petro Poroshenko welcomed the decision, writing on Facebook it was "confirmation of the correctness of the strategy we have chosen."
Zerkal urged Russia to "conform swiftly and wholly" with the ruling, which now faces going to arbitration.
But Russia, which accused the sailors of violating its maritime borders, showed no sign of doing so even after a ruling which increases the pressure on Moscow with regard to its relations with Kiev.
- Russia digs in -
"In the course of the forthcoming arbitration proceedings we will constantly defend our position," a Russian foreign ministry statement said.
The situation could have been avoided "under the conditions of following Russian law regarding navigation in this area," the ministry wrote.
The statement added that statements by both nations as they ratified the 1982 law of the sea "exclude the possibility of using the dispute resolution procedures laid out by the convention."
US Secretary of State Mike Pompeo on his recent visit to Moscow urged the Kremlin to make a gesture to end the impasse.
French President Emmanuel Macron and German Chancellor Angela Merkel telephoned Russian President Vladimir Putin last Tuesday to push for dialogue, just two days after Zelensky, a comedian, was invested in Kiev.
The Ukrainian sailors face up to six years in prison if found guilty in what Kremlin critics have warned could be a show trial.
The sailors saga is a sideshow in Russia's five-year conflict with its neighbour which started with Moscow's March 2014 annexation of Crimea. Since then, fighting between pro-Russian separatists and Kiev government forces in Ukraine's east has claimed around 13,000 lives, according to UN figures.