NATO Secretary General Anders Fogh Rasmussen on Wednesday said the 28-nation alliance will immediately deploy forces to the region. "We will have more planes in the air, more ships on the water, more readiness on land" while alliance defense plans will be "reviewed and reinforced."
Rasmussen did not specify the number of troops or assets that will be deployed, but said only it will be "enough." However, Rasmussen also said that NATO hopes Thursday's talks in Geneva will "pave the way for a peaceful and political solution to the crisis."
Envoys from the EU, US, Russia and Ukraine are scheduled to attend the talks.
Meanwhile, earlier on Wednesday, armored personnel carriers were seen in the eastern Ukrainian town of Slovyansk, eyewitnesses told new agencies.
Several armed men wearing mismatched battle fatigues sat atop each of the vehicles and were reportedly enthusiastically greeted at pro-Russian checkpoints outside the city.
Several government buildings in Slovyansk, which is located in the Donetsk region that borders Russia, are being occupied by pro-Russian separatists. The protesters are demanding broader autonomy for their eastern Ukraine region and closer ties with Moscow.
Slovyansk is about 15 kilometers (9 miles) north of the town of Kramatorsk, where an AFP photographer also reported seeing Russian flag-bearing combat vehicles. It remains unclear whether both sightings were the same group of personnel carriers.
On Tuesday, Kyiv launched a military operation against armed pro-Russian separatists after they refused to vacate government buildings in at least nine cities in eastern Ukraine by a Monday deadline.
Ukraine's interim Prime Minister Arseny Yatsenyuk on Wednesday accused Russia of "exporting terrorism" to Ukraine.
"The Russian government must immediately call off its intelligence-diversionary groups, condemn the terrorists and demand that they free the buildings," Yatsenyuk told a government meeting.
He also accused Moscow of erecting a new "Berlin Wall" that threatens European security.
"Today's events... are starting to endanger Europe and the European Union. It is now clear that our Russian neighbors have decided to build a new Berlin Wall and return to the Cold War era," he added.
hc/dr (Reuters, AFP, AP, dpa)