Denying the presence of Russian forces in Donbas is a standard pro-Kremlin disinformation narrative. 

According to the US Defense Intelligence Agency (DIA), Russian special forces and troops operated to mobilize, lead, equip, and support separatist militias in the Donbas region of eastern Ukraine from spring 2014 to the present, although their presence was denied by Moscow. Overwhelming evidence confirms that Russia participates in the conflict with Ukraine sending mercenaries to Donbas.  

In an interview, delivered in autumn 2018, former First Deputy Chief Monitor to the Organization for Security and Co-operation's Special Monitoring Mission to Ukraine Alexander Hug mentions that the Mission has been recording the instances of Russia's involvement into the war in Donbas. "We have been seeing at least in six instances convoys leaving and entering Ukraine, which we have been documenting, which have been driving towards the unsecure border with the Russian Federation in the middle of the night, on dirt roads, and have been seen at the unsecure border at areas where there is no official border crossing," Hug said. 

The war in Eastern Ukraine was provoked by Russia. There is irrefutable evidence of direct Russian military involvement in Eastern Ukraine. 

For similar debunks, see here.