'President Poroshenko signed a law to approve the decree 'on the introduction of martial law in Ukraine', Tsegolko wrote on Twitter.
Earlier in the day, the Ukranian president warned that the country was on the brink of 'a full-scale war with the Russian Federation'.
The news comes amid the recent conflict in Kerch Strait. According to Russia's Federal Security Service (FSB), Ukrainian ships crossed the Russian maritime border on 25 November and were seized by the Russian Border Guard due to the lack of a reply to a lawful demand to stop.
The Russian Foreign Ministry has described the Ukrainian vessels’ actions as a provocation committed in violation of international law.