Pasi Eronen is an analyst at The Conflict Studies Research Centre, which specializes in Eurasian security. The opinions in this article belong to the author.

(CNN) A few days after the fifth anniversary of Euromaidan -- the wave of demonstrations that kicked off in Ukraine in November 2013 -- vessels belonging to the Russian Coast Guard opened fire against three Ukrainian Navy ships, according to Ukraine's military, that were trying to pass through the Strait of Kerch.

Ukraine said the firefight ended with six of its servicemen wounded and Russian Special Operations Forces capturing the vessels, along with their crews of 23.

The captured ships and crews were then transported to a nearby Russian base.

The clash presents a dangerous new escalation in a conflict that has caused thousands of casualties and deaths since the 2014 illegal annexation of Crimea by Russia and the subsequent fighting that erupted in Eastern Ukraine.

While Russian President Vladimir Putin later admitted that Russian troops were present in Crimea, Sunday's hostilities are the first time that conflict has openly and undeniably taken place between Ukrainian forces and operatives flying the Russian flag since 2014.

Read More