U.S. Special Representative for Ukraine negotiations, Ambassador Kurt Volker, and U.S. Ambassador to Ukraine Marie Yovanovitch have called on Russian authorities to release all 24 Ukrainian sailors held by Russia.

In a tweet posted Tuesday, the U.S. Embassy in Ukraine wrote that Volker and Yovanovitch met with Ukraine's Defense Minister Stepan Poltorak, and "reinforced that Russia’s aggression is unacceptable.

"Russia should release the Ukrainian crewmembers, return Ukrainian vessels, and not impede maritime transit to and from Ukrainian ports," the statement reads.

UNIAN memo. On the morning of November 25, Russia blocked the passage through the Kerch Strait of the Ukrainian Navy's Yany Kapu tugboat and two small artillery boats, Berdyansk and Nikopol. The boats were on a scheduled redeployment from the Black Sea port of Odesa to the Azov Sea port of Mariupol.

As Ukrainian vessels were leaving the Kerch Strait area to return to Odesa, Russian ships opened aimed fire on them. Russia captured 24 Ukrainian sailors, including three injured in the attack, and seized the vessels.

The detained sailors, who Ukraine firmly insists must be treated as POWs, given Russia's armed attack on Ukrainian Navy boats, were accused of "illegally crossing the Russian border" and are now facing up to six years in prison.

Russia-controlled "court" in the occupied Crimea ruled to remand all sailors in custody. The Ukrainians were subsequently transferred to Moscow-based detention facilities.