Ukraine voted to impose martial law Monday after a naval confrontation with Russia over the weekend in which Kremlin forces fired on and seized three Ukrainian vessels.
The Associated Press reported that the move was made to fight what Ukrainian President Petro Poroshenko has called "growing aggression" from Moscow.
Russian fire injured two Ukrainian sailors and hit two vessels on Sunday off the disputed Crimean Peninsula.
Kremlin vessels then took the two ships, which had been struck as well as a tugboat, according to Ukrainian authorities.
Russia blamed Ukraine for the dispute Sunday.
Kremlin spokesman Dmitry Peskov said Russian ships were reacting to an "incursion" by Ukrainian boats.
The United Nations Security Council held an emergency meeting Monday afternoon to discuss the clash.
Russia annexed Crimea from Ukraine in 2014, inviting international backlash and sanctions.