Ukrainian President Petro Poroshenko has accused Russia of launching a "direct and open aggression" against Ukraine.
He added there would be "high-level personnel changes" within the Ukrainian armed forces in light of the events of the past few days.
This is in spite of ceasefire negotiation talks due to take place later today.
Were the Russians -as Barack Obama claims - weighed down by sanctions, or where the Ukrainians looking to cut their losses?
The new president of the European Council could be "very important" for David Cameron.