Five separatists were killed during the operation.
Ukraine accuses Russia of backing and instigating the separatists.
Russia denies that they have any part in it, but have repeatedly stated their "right" to "defend" Ukrainians of Russian descent.
They used the same argument during their seizing of Crimea, in March.
As many as fifty thousand Russian troops are encamped just east of the border.
On Thursday, in response to the Slovyansk raid, Russian Defense Minister Sergei Shoigu announced that the Russian troops will conduct more military exercises.
