"We believe that Russian generals are involved in the conflict in the Donbas, and that the Russian officers command tactical military operations in the Donbas. We know that Russia is using modern electronic missile guidance systems of the air-to-surface class," he said.

"We know that the regular troops of the Russian army took part in the occupation of Debaltseve, and in military actions that continued even after the Minsk agreements had to come into force. Russia has delivered hundreds and hundreds of pieces of heavy weapons since December, since the ceasefire, in particular those used in the attack on Debaltseve," Pyatt said.

"This conflict may be ended by one phone call - a call by Russian President Vladimir Putin," Pyatt said.

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Russia denies being involved in the conflict in the east of Ukraine, although the Ukrainian government, the Ukrainian armed forces, volunteers and representatives of the West countries have presented a large amount of evidence of Russian military involvement in the Donbas conflict.