Ukrainian President Petro Poroshenko signed a decree on Monday to introduce martial law for 60 days, a statement on his website said, though it needs parliamentary approval to come into force.
The decision came a day after Russia fired at and captured three Ukrainian vessels, triggering a sharp escalation in tensions between the two countries.
Parliament was expected to debate the decree later on Monday though a televised session of a parliamentary committee unanimously supported it.
Ukrainian legislation on martial law allows for a slew of curbs, including restrictions on movement and peaceful assembly, curfews, and restricting the media, though Poroshenko’s decree made no specific references to such restrictions.
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Eleven measures outlined in the decree provide for mobilizing reserve forces, organizing the air defense of important state facilities and taking urgent steps to bring in enhanced cyber security measures and ensure public order.
There was no mention of a presidential election due to be held in March. Poroshenko’s move has prompted speculation by critics and opposition politicians that he might use it to delay the vote.
A twelfth provision of the decree was not published.
Russia is holding 24 Ukrainian sailors who were detained on board three navy ships in the Kerch Strait on Sunday, Interfax news agency cited Russian human rights commissioner Tatyana Moskalkova as saying on Monday.
She said three of the sailors were wounded in the incident and were recovering in hospital, but that they were not in a critical condition.
Russia seized two small Ukrainian armoured artillery vessels and a tug boat, which Moscow said had illegally entered Russia's territorial waters. Kiev said its vessels did nothing wrong and has accused Russia of military aggression.