KIEV, November 27. /TASS/. The Ukrainian Armed Forces units deployed to Donbass have been put on full combat alert, the press center of the so-called "combined forces operation" said in a Facebook statement on Tuesday.

"In compliance with an order issued by Combined Forces Operation Commander Sergei Nayev, military servicemen have increased vigilance, armed units have been put on full combat alert," the statement reads.

On Monday, Ukraine’s General Staff ordered to put the country’s Armed Forces on full combat alert.

In addition, a 30-say martial law was declared in the Vinnitsa, Lugansk, Nikolayevsk, Odessa, Sumy, Kharkov, Chernigov, Donetsk, Zaporozhye and Kherson regions, as well as in Ukraine’s territorial waters in the Sea of Azov, starting from November 28.

A Sunday incident in the Kerch Strait was used as an excuse for these steps. On November 25, three Ukrainian navy ships - the Berdyansk, the Nikopol and the Yany Kapu - illegally crossed Russia’s border and tried to carry out some illegal actions in Russian territorial waters on Sunday night. They ignored legitimate demands to stop issued by vessels belonging to the FSB Border Service and the Black Sea Fleet and continued maneuvering dangerously. In order to stop the Ukrainian ships, weapons had to be used. The three vessels were detained in Russian territorial waters. Three Ukrainian military servicemen suffered light wounds and were provided with medical assistance. A criminal investigation has been opened into the border incident.

Moscow slammed the incident as a provocation. The European Union and NATO called for a de-escalation, while Kiev declared martial law.