NATO Secretary-General Anders Fogh Rasmussen has said he was "extremely concerned" about the escalation of tensions in eastern Ukraine.
In a statement on April 13, Rasmussen denounced a “concerted campaign of violence by pro-Russian separatists, aiming to destabilize Ukraine as a sovereign state."
Drawing parallels with Ukraine’s Crimea region, which Russia annexed last month after deploying forces there, Rasmussen added: "The reappearance of men with specialized Russian weapons and identical uniforms without insignia, as previously worn by Russian troops during Russia's illegal and illegitimate seizure of Crimea, is a grave development.”
Rasmussen called on Russia to "de-escalate" the situation and to pull back its troops from the area around Ukraine's border.
"Any further Russian military interference, under any pretext, will only deepen Russia's international isolation," he added.