About 8,500 Russian troops are taking part in military exercises near the border with Ukraine involving artillery and multiple rocket launchers, the Russian Defence Ministry said on Thursday.
A statement on the ministry's website confirmed that the exercises had begun at bases in the Southern Military District but did not say how long they would last.
Barack Obama warned Russia that the West will be forced to apply a cost to Moscow if it fails to change course in its dispute with Ukraine.
The ballot paper that the people of Crimea will use in Sunday's referendum was published today
Vitali Klitschko's visit to the eastern city of Donetsk is clearly an attempt to try to ease the divisions with Ukraine.