A U.N. court is considering a legal case brought by Ukraine over the capture of 24 sailors and three naval vessels held by Russia since November.

The Hamburg-based International Tribunal for the Law of the Sea began its two-day hearing Friday.

Ukraine is demanding the immediate release of its sailors and ships, arguing that failure to do so would breach the country's rights.

Russia argues that the sovereignty rights Ukraine claims in the case don't apply because they are covered by a military exception.

The confrontation the Kerch Strait linking the Sea of Azov with the Black Sea marked a flashpoint in the simmering conflict over Russia's 2014 annexation of the Crimean Peninsula. Russia seized Crimea in a move that Ukraine and most of the world views as illegal.