Ukraine's parliament is to decide whether to bring in martial law, after Sunday's capture of three of its naval vessels and 23 crew members by Russia.
The three ships were sailing off the coast of Crimea, which was annexed by Russia in 2014, when they were seized.
Russia opened fire, before its special forces stormed the vessels.
Between three and six Ukrainians were injured.
Ukraine said it was a Russian "act of aggression".
Moscow said the ships had illegally entered its waters.
This is the first time the two militaries have come into open conflict in recent years, although Ukrainian forces have been fighting Russian‑backed separatists and Russia volunteers in the east of the country.
A number of Western countries condemned Russia's actions, and the UN Security Council is due to hold an emergency meeting.
[Source:BBC News]
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