Nato: Russia had illegally crossed Ukraine's border
29 August 2014 Last updated at 22:39 BST
Nato has accused Russia of blatantly violating Ukraine's sovereignty by sending troops and weapons over the border.
Russia's President, Vladimir Putin, denies it and has blamed Ukraine for the crisis, comparing its actions to those of Nazi Germany during World War Two.
Since fighting began in April more than 2,500 people have been killed.
Bridget Kendall reports.