Ukrainian President Petro Poroshenko. [File photo: VCG]

Ukrainian President Petro Poroshenko on Monday called on Russia to release the Ukrainian sailors who were detained during the latest confrontation in the Sea of Azov.

"I appeal to the leadership of the Russian Federation, demanding the immediate release of Ukrainian servicemen who, in violation of international law, were brutally detained and whose fate is unknown," the Ukrainian president's press service quoted him as saying.

On Sunday, the Ukrainian Navy said that Russian forces opened fire and seized three Ukrainian ships near the Kerch Strait which separates the Black Sea and the Sea of Azov.

Russia's Federal Security Service (FSB) said that the three Ukrainian ships, namely Berdyansk, Nikopol and Yany Kapu, breached the Russian border and conducted dangerous maneuvers despite calls from Russian vessels that accompanied them to avoid advancing.

The Ukrainian Navy said it had informed Russia in advance about the passage of the Ukrainian vessels from the Black Sea to the Sea of Azov through the Kerch Strait, calling Russia's actions an "act of aggression."

The General Staff of the Ukrainian Armed Forces said that 23 Ukrainians were detained during the tensions.

The Ukrainian Navy said that six Ukrainian military sailors were wounded in the standoff and two of them were in serious condition.

Meanwhile, Russia said three Ukrainian soldiers were slightly wounded and have received medical assistance.