Nato Secretary General Jens Stoltenberg has rebuffed Russian President Vladimir Putin's claim that the Ukrainian army operates as a "foreign legion" for the alliance, calling it "nonsense".
According to the BBC, Stoltenberg also called on Russia to stop providing military support to pro-Russian rebels.
The Russian leader accused Ukraine's army of operating against the country's national interests by wanting to contain Russia, the report said.
Ukraine has been witnessing incessant violence with a series of deadly attacks taking place in the eastern part of the country over the past week.
At least 30 people were reported dead and dozens were wounded in repeated rocket hits in the Azov Sea city of Mariupol on Saturday.