A UN maritime tribunal ruled Saturday that Russia must immediately release three Ukrainian naval vessels it captured and free the 24 sailors it detained.

"The Russian Federation must proceed immediately to release the Ukrainian soldiers and allow them to return to Ukraine," said Jin-Hyun Paik, a judge of the International Maritime Court in the German city of Hamburg.

The sailors and naval vessels were seized by Russia off the Crimean Peninsula in November 2018, which was the most dangerous direct clash in years between Russia and Ukraine. The two countries have been in conflict for more than five years over the 2014 incorporation of the Crimean Peninsula by Russia.

Ukraine's former president Petro Poroshenko insisted the sailors were "prisoners of war" and described their detention as "blatant proof that Russia continues to show cynical disrespect for human rights."

Three Ukrainian ships are docked near the Kerch after being seized, in Kerch, Crimea, November 26, 2018. /AP Photo Three Ukrainian ships are docked near the Kerch after being seized, in Kerch, Crimea, November 26, 2018. /AP Photo

Moscow has accused the sailors of violating its maritime borders, and lawyers have said they could face up to six years in prison.

Kiev on May 10 asked the international tribunal to order Russia to release the sailors and the Berdyansk, Nikopol and Yani Kapu vessels.

The tribunal's decision was a 19-1 vote with only the Russian judge supporting Moscow and its decisions are legally binding, but have no power to enforce them. It called for both sides to report back on their compliance by June 25 and urged both parties to "refrain from taking any action which might aggravate or extend the dispute."

Volodymyr Zelensky, Ukraine's newly elected president, said Saturday that the compliance of Russia on this issue could be a first signal of "real readiness to stop the conflict with Ukraine."

"In this way, Russia could take a step toward unblocking talks and resolving in a civilized way problems that it created," Zelensky said on Twitter.

Ukraine's new President Volodymyr Zelensky during his inauguration ceremony in the parliament hall in Kiev, Ukraine, May 20, 2019. /VCG Photo Ukraine's new President Volodymyr Zelensky during his inauguration ceremony in the parliament hall in Kiev, Ukraine, May 20, 2019. /VCG Photo

Ukrainian foreign ministry spokeswoman Kateryna Zelenko told AFP she hoped for judicial support to help "break the deadlock on the release of sailors and military vessels."

Russia didn't immediately specify what it would do on the release of ships and sailors, but has denied any wrongdoing and said it does not recognize the jurisdiction of the court.

Bogdan Bezpalko, a member of the Kremlin's International Relations Committee, said recently on Sputnik Radio that "Russia has not violated international law; Russia has reacted to an aggression against it."

Russian Foreign Ministry said in a statement that it would consistently defend its position, including the lack of jurisdiction, in the subsequent arbitration proceedings at the tribunal.

(With input from AP, AFP and Reuters)