The Russian military has been carrying out exercises close to the border with Ukraine.
Russia’s defence ministry confirmed 8,500 troops were taking part in drills in several regions along the border.
In Rostov-on-Don where the ousted Ukranian president Yanukovych has been staying, riffles, machine guns and rocket propelled grenades were used.
It comes as Moscow warned it would reciprocate with sanctions against the EU and US if they imposed them first.
“I would like to stress that Russia was not the initiator of the circumstances that we are talking about…” Russian President Vladimir Putin said.
Meanwhile, in a show of strength, NATO is making its presence felt on the other side of Ukraine, beginning surveillance flights over Poland and Romania.
The US has also sent fighter jets to take part in the exercise.