"Held a meeting with the leadership of defense agencies and the foreign ministry…ordered to put all units near the administrative border with Crimea and along the entire line of contact in Donbass on high readiness," Poroshenko said on Twitter.
The move comes a day after the Russian Federal Security Service said it had foiled terrorist attacks in Crimea organized by the Ukrainian main intelligence directorate, and stamped out a spy ring detaining both Russian and Ukrainian nationals involved in the plot. Two Russian officers were killed.
The Minsk deal on Ukraine's reconciliation was struck in February 2015 by Russia, Ukraine, Germany and France and later signed by Kiev and the Donbass self-proclaimed republics of Donetsk and Lugansk. Both warring parties have repeatedly accused each other of violating the truce despite agreeing to the ceasefire deal.
Crimea rejoined Russia after a 2014 referendum in which over 96 percent of the Crimean population voted in favor of reunification. Sevastopol, which has a federal city status, supported the move by 95.6 percent of the votes.