Gen Oleksandr Tarnavskyi says his forces are struggling to overcome multi-layered minefields and fortified defensive lines.
"That is why most of the tasks have to be performed by troops."
He says Russia's military has displayed "professional qualities" by preventing Ukrainian forces from "advancing quickly".
"I don't underestimate the enemy," he adds.
Gen Tarnavskiy said his forces were doing "hard and painstaking work". He said "any defence can be broken but you need patience time and skilful actions".
Ukraine was slowly wearing down their enemy, he said. Russia didn't care about losing men, and recent changes in their military leadership "means everything is not OK", he added. He insisted that Ukraine had yet to commit its main strike force.
"Slow or not, the offensive is taking place and it will definitely reach its goal," he says.
I ask Gen Tarnavsky how we can judge whether it's a success or a failure?
He smiles and replies: "If the offensive were not successful, I wouldn't be talking to you now."
