The U.S. Department of State published a statement on 22 April saying that the Russian military has continued moving heavy weapons and additional troops to the Ukrainian border, and has deployed additional air defense systems into eastern Ukraine, creating the highest concentration of air defenses in the area since the height of the conflict last August. Russian and Russia-backed separatist forces have been conducting increasingly complex training in eastern Ukraine. Also NATO Secretary General said Russia is building up forces along the Ukrainian border and actively delivering weapons and supplies to eastern Ukraine militants, which allows them to start rapid attacks. Meanwhile the United States and Russian officials are waging a war of words, with each accusing the other of threatening to undo the ceasefire.