Ukraine is mounting "counter-attacks, with which one can win back places or individual areas of the frontlines, but not push Russia back over a broad front", General Eberhard Zorn told the forthcoming edition of magazine Focus.

Moscow has been forced to pull back troops from swathes of the northeast, particularly in the Kharkiv region, following Kyiv's dramatic assault since the beginning of September to wrest back terrain.

The territorial shifts marked one of Russia's biggest setbacks since its troops were repelled from Kyiv in the earliest days of the nearly seven-month-long war.

Ukrainian troops were also seeking to take back territories in the south, but progress has been slower than in the northeast.

Zorn warned that the Ukrainian forces might become overstretched if they were engaged in simultaneous counter-offensives, noting that they would need outnumber the Russians by "three to one".

At the same time, the German army chief acknowledged that the Ukrainian military is conducting its operations "masterfully and very agilely.

"Two weeks ago, I would have said that the entire Donbas (region) would be in Russian hands in six months. Today I say -- they won't manage that," he said.

Zorn also defended German weapons deliveries to Ukraine, as Berlin came under pressure again for its refusal to send battle tanks despite Kyiv's pleas.

The general underlined that the armaments that Germany has delivered so far "is considerable, both in quantity and quality".

He warned however that the German military had to be careful its own stocks did not run low. "Everything we give away, we need back," he said.

His comments came a day after Ukraine's Foreign Minister Dmytro Kuleba slammed "disappointing signals from Germany" on the supply of more armaments, including battle tanks.

After initially refusing to provide Kyiv's forces with lethal weapons at the outbreak of war, Germany has since increased its arms deliveries to Ukraine.

Kyiv says since the beginning of September its forces have retaken hundreds of villages, towns and cities that had been captured by Russian forces that invaded Ukraine in February.

Moscow said Wednesday that its forces were hitting back on areas recaptured in Kharkiv with "massive strikes".