"We have precise information that Russia is present in eastern Ukraine and that it has delivered large quantities of heavy, advanced weapons to the separatists," NATO Secretary-General Jens Stoltenberg told reporters in Oslo, Censor.NET reports citing Reuters.
"Artillery, anti-aircraft systems, advanced weapons systems. They have supplied more than 1,000 units of this kind to the separatists," he said.
"Russia has a particular responsibility (to end the conflict) because they back the separatists and supply them with heavy arms. They also have forces in eastern Ukraine," Stoltenberg added.