More than 8,000 Russian troops have begun military exercises close to the border with Ukraine.
Russian defense ministry confirmed that artillery such as rocket launchers and anti-tank weapons would also be involved in the exercises.
They come at a time of high tension ahead of Crimea’s referendum on Sunday on whether to join Russia.
Ukraine PM Arseniy Yatsenyuk has told the UN Security Council his country is a victim of Russian aggression.
Arseniy Yatsenyuk said it was “absolutely and entirely unacceptable, in the 21st Century, to resolve any kind of conflict with tanks artillery and boots on the ground”, in reference to Russian troops at key sites in Crimea.
Meanwhile, reports from the eastern Ukrainian city of Donetsk say at least one person has been killed and several wounded in clashes between hundreds of pro- and anti-Moscow demonstrators.
Russia confirmed that military exercises had begun in the regions of Rostov, Belgorod and Kursk, which are close to the border of Ukraine, and would continue until the end of March.
“The main aim… is a multi-faceted check of the units’ cohesiveness followed by the performance of battle training assignments in unfamiliar terrain and untested firing ranges,” the Russian defense ministry said.
In a sign the tension may be spreading, Belarus – a Russian ally – confirmed Moscow had deployed, at its request, extra fighter jets and military transport aircraft after Nato boosted its forces in the neighboring Baltic countries.
Russian President Vladimir Putin told a meeting of his Security Council that this was an inter-Ukrainian crisis that “arose not through our fault, but we are involved in it, one way or another”.
He said he wanted to discuss how to “build relations with our partners and friends in Ukraine and our other partners in Europe and the United States”.
Separately, the Organisation for Security and Co-operation in Europe (OSCE) said Russia had now given its support to a possible long-term monitoring mission in Ukraine.
[youtube vJtXG6FK130 650]