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 tension between the two countries. Moscow accused the vessels of illegally entering its waters in the Azov Sea.

Ukraine's parliament is expected to debate the decree later on Monday.

NATO will hold an emergency meeting with Ukrainian officials at alliance headquarters in Brussels on Monday over the naval standoff off the coast of Crimea. The United Nations Security Council will also hold an emergency meeting over the issue on Monday.

China urges restraint on both sides in order to prevent an escalation in tensions, Chinese Foreign Ministry spokesman Geng Shuang said at a regular press briefing on Monday, adding that the dispute should be resolved through dialogue and consultation.

The Azov Sea, scene of the new escalation in tensions between Russia and Ukraine, is joined to the Black Sea by the Strait of Kerch, a narrow strip that acts as a vital shipping lane for both nations. 

A treaty signed between Russia and Ukraine in December 2003 agreed on common management of the Azov Sea and the 15-kilometer-wide strait. It did not, though, demarcate the maritime border between the two countries. 

(With inputs from agencies)

(Cover: Ukrainian far-right groups attend a rally as they burn flares demanding to set martial law in the country and to cut diplomatic relations with Russia in front of the Ukrainian Parliament in Kiev, November 26, 2018. /VCG Photo)