Military spokesman Igor Konashenkov told state television that forces of the Donetsk People's Republic gained "up to three kilometres" (1.8 miles) in territory and those of the Lugansk People's Republic "advanced one and a half kilometres."

He added that Russia had "high precision weapons" and that Ukrainian civilians had "nothing to fear."

Konashenkov said the Russia-backed rebel troops are "now fighting and inflicting ... damage on the enemy."

Russian President Vladimir Putin announced he was launching an offensive on Ukraine in the early hours of Thursday.

He did so after recognising the two rebel republics in eastern Ukraine and signing friendship treaties with them.