Ukraine appealed for assistance from NATO on Saturday, asking it to use all possible measures to ensure its territorial integrity and protect its people.
The call came hours after the Federation Council approved the deployment of military forces in Ukraine, in response to what Moscow claims is the threat being leveled against its servicemen and Russian citizens in the southern Crimea Peninsula.
Authorities in Ukraine have sounded the alarm over what they are calling an unwarranted act of aggression.
In addition to asking for NATO's protection, Ukraine's Foreign Minister Andrei Deshchitsa urged the trans-Atlantic military alliance to aid it in securing nuclear facilities based in Ukraine, local news agency UNN reported.
The North Atlantic Council, NATO's main governing body, was to hold an extraordinary meeting on Sunday to discuss events in Ukraine, the military bloc's secretary general, Anders Fogh Rasmussen, said on Twitter.
Russia has adopted increasingly combative rhetoric on Ukraine ever since an opposition movement in the country last week toppled President Viktor Yanukovych after weeks of sometimes violent protests.
Moscow accuses the West of backing the Ukrainian uprising, which it says has been directed by violent and politically extremist radicals.
On Saturday, Deputy Foreign Minister Grigory Karasin expressed the hope that the international community would apply pressure on Kiev to normalize the situation.
In addition to acting as home to Russia's strategically valuable Black Sea Fleet base, Crimea also has a substantial ethnic Russian community.
Politicians in Moscow have urged their government to act firmly on behalf of Russians in Crimea, many of who have apparently expressed a preference for the region to be annexed by their eastern neighbor.
Deshchitsa said a settlement for the situation in Crimea should be peaceful.
"We must not allow the use of force and provocations," he said.