KYIV, Nov 26 - Much of Ukraine will introduce martial law after Russia fired on and seized three of its naval ships in the Black Sea, prompting warnings of a dangerous escalation in their four-year conflict and strong western condemnation of Moscow.

Ukraine’s parliament on Monday approved the decree issued by President Petro Poroshenko, who said his nation must react to a “new phase of aggression” and face the “extremely serious threat of a land-based operation” by Russian forces, the Irish Times reported.

Poroshenko said martial law would apply to 10 “high-risk” border regions, starting on Wednesday and lasting for just 30 days, so as not to effect presidential elections due in March and to ease concern that he might try to postpone the vote. He insisted that the special measures would “allow us, in the event of invasion, to react and mobilize all resources as quickly as possible” and would not bring “restrictions on the rights and freedoms of citizens or the introduction of censorship.”

However, critics still saw politics behind Poroshenko’s decision to take this step now, four years after Russia annexed Crimea and launched an undeclared war in eastern Ukraine that has claimed more than 10,300 lives.

Moscow did not respond to calls from Ukraine and its allies to free the three ships and 23 sailors Russian forces captured on Sunday near the Kerch Strait, which links the Black Sea with the smaller Sea of Azov off the coast of Crimea.

The two countries blamed each other for the incident, which involved a Russian naval ship ramming a Ukrainian vessel before Russian ships pursued the Ukrainian boats, shot at them and forced them to stop, injuring six Ukrainian sailors in the process. The boats were then tugged to the Crimean port of Kerch.

Russia said Ukraine’s ships illegally entered its territorial waters, but Kiev accused Moscow of flagrant aggression and released what it called intercepted radio messages in which Russian officers discuss how best to attack and disable the Ukrainian boats. (it/ez)