NATO's chief has dismissed as "nonsense" a claim by Russia's Vladimir Putin that the Ukrainian army operates as a "foreign legion" for the alliance.
Nato Secretary General Jens Stoltenberg also called on Russia to stop providing military support to pro-Russian rebels.
President Putin said Ukraine's army was operating against Ukrainian national interests by seeking to contain Russia.
Violence in eastern Ukraine is at its worst level for months, with a series of deadly attacks over the past week.
The military said early on Monday that seven Ukrainian soldiers had been killed fighting Russian-backed separatists in 24 hours.
It said the heaviest fighting was continuing around the town of Debaltseve.
On Saturday, a series of rocket attacks left 30 people dead and many more injured in the Azov Sea city of Mariupol.