NATO on Friday accused Russia of a "blatant violation of Ukraine's sovereignty" and urged it to immediately cease its "illegal military actions" in eastern regions of the country.

NATO Secretary General Anders Fogh Rasmussen said despite "hollow denials" by Russia, it was clear it was involved in "direct military operations" in Ukraine.

"We condemn in the strongest terms Russia’s continued disregard of its international obligations. We urge Russia to cease its illegal military actions, stop its support to armed separatists, and take immediate and verifiable steps towards de-escalation of this grave crisis," Rasmussen said in a statement.

Rasmussen's statement came after NATO convened an emergency meeting Friday in Brussels, Belgium, over the crisis at the request of Ukrainian authorities.

This week, the rebels have opened a new front in the cities of Amvrosiivka and Starobeshevo. One fear is that Russia is attempting to create a land link between Russia and the strategic peninsula of Crimea, which Russia annexed with special forces troops in March. Poroshenko said Russian troops are leading a separatist counteroffensive in the east, bringing in tanks and firing artillery from inside Ukrainian territory.



On Thursday, Ukrainian President Petro Poroshenko said Russian troops had crossed the border and were fighting on the side of the pro-Russian separatists. NATO subsequently backed up his allegations, releasing satellite photos it said showed Russian forces and artillery inside Ukraine. NATO said more than 1,000 Russian troops were fighting in Ukraine.

"Despite Moscow’s hollow denials, it is now clear that Russian troops and equipment have illegally crossed the border into eastern and south-eastern Ukraine. This is not an isolated action, but part of a dangerous pattern over many months to destabilize Ukraine as a sovereign nation," Rasmussen said Friday.

"Russian forces are engaged in direct military operations inside Ukraine. Russia continues to supply the separatists with tanks, armored vehicles, artillery and rocket launchers. Russia has fired on Ukraine from both Russian territory and within Ukraine itself. Moreover, Russia continues to maintain thousands of combat-ready troops close to Ukraine’s borders. This is a blatant violation of Ukraine’s sovereignty and territorial integrity. It defies all diplomatic efforts for a peaceful solution."

Ukrainian Prime Minister Arseny Yatsenyuk said Friday that Ukraine would attempt to become a member of NATO, something that could further increase tensions with Russia, which wants to maintain influence over its neighbor. Yatsenyuk said Ukraine's priority remains membership in the European Union.