A Ukrainian serviceman patrols near the frontline in the fight against Russian-backed separatists near the small city of Marinka, Donetsk region

Video. Russia says buildup at Ukraine border is a response to NATO 'threats'

The comments come after a surge of cease-fire violations in eastern Ukraine, where Russia-backed separatists and Ukrainian forces have been locked in a conflict since Moscow’s 2014 annexation of Crimea.