Despite military significant assistance from Western countries to Ukraine that will allow it to de-occupy territories, one cannot underestimate Russia's preparations, in particular, to create defensive lines, NATO Secretary General Jens Stoltenberg has said.

"We should never underestimate the Russians. The front line has been static for a long time, the Russian forces have been able to build significant defensive lines to counter the planned counteroffensive of the Ukrainian Armed Forces," he told CNN.

Stoltenberg noted that wars are inherently unpredictable, but Ukraine has already shown that it can de-occupy territory that was under Russian control.

According to the NATO Secretary General, all the weapons and training for Ukrainians from NATO countries, including nine well-trained and equipped brigades, should help free more territory from the occupiers during the counteroffensive.