A senior Ukrainian army general says frontline Ukrainian troops face shortages of artillery shells and have scaled back some military operations.

Reuters news agency on Monday quoted Brigadier General Oleksandr Tarnavskyi as saying "there is a problem with ammunition."

Tarnavskyi -- who is leading the counteroffensive against Russian forces -- said the volume of aid coming in is not sufficient for Ukrainians, and that Russian attacks continue constantly.

He said Ukrainian forces cannot keep their strength in all frontline areas. He said his troops move to defense in some areas, while they continue offensive actions in others.

During a panel discussion on Sunday, Ukraine's defense intelligence chief Kyrylo Budanov said mobilization is necessary for Ukraine's military to maintain current force levels.

He stressed the need to address the issue of Ukrainian men evading conscription. He said there is almost zero efficiency in the conscription system if authorities fail to give them the motivation to join the troops.