On November 25, Russian coastal patrol craft intercepted and captured three Ukrainian vessels off the coast of Crimea while they were trying to navigate through the Kerch Strait, which connects the Black Sea with the Sea of Azov, and which is now crossed by a Russian bridge leading to the Moscow-annexed Crimea.
A total of 24 Ukrainian sailors were captured and held prisoner for violating Russian national waters.
Declaring the incident an open act of aggression, Poroshenko issued an executive proposal for martial law, which was approved by the Verkhovna Rada, the Ukrainian parliament.
Once the order came into force, additional troops were sent to patrol the Russian borders, reservists were mobilized and male Russian citizens aged from 16 to 60 were barred from entering Ukraine. The latter measure, the president said, serves the purpose “of preventing infiltration by Russian military intelligence and potential militants.”
Leonid Litra, a Senior Research Fellow at the New Europe Center, said the naval clash on the Kerch Strait left Poroshenko with little choice other than martial law; a milder reaction would have meant political suicide.
“Poroshenko had to have a strong reaction, since any weakness at times when Ukraine is attacked could have cost him a loss of credibility among his electorate and lowered even more his chances to get re-elected”, Litra said.