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Most definitely. They have to take lot of other things first until they can cut off Kharkov.
I think they don't want to launch such a mobile assault. They become wary after the losses they suffered at the beginning of the war. How the columns were trapped. They can't hide such a large force either. NATO intelligence informs Ukraine. Satellites see everything. 
I also think Kharkov is fortified and ways leading around too. Perhaps what the Ukrainians are lacking is the troops to man the trenches, bunker, and forts.