NATO Secretary-General Jens Stoltenberg looks on during a press conference with the German chancellor following their meeting at the Chancellery in Berlin on December 1, 2022. AFP
Ukrainian forces have been pushing a counter-offensive in which they have made significant gains in the east and south, including Kyiv's retaking of the city of Kherson.
"What we see now is that Russia is actually attempting to try to have some kind of freeze of this war, at least for a short period of time, so they can regroup, repair, recover and then try to launch a bigger offensive next spring," Stoltenberg told a public event hosted by the Financial Times.
Stoltenberg said NATO members were continuing their "unprecedented" supply of arms and support to Ukraine despite concerns that the conflict is draining Western stockpiles.
"As important as adding new systems, is to ensure that systems or weapons we have already delivered, are actually operational or working in an effective way," Stoltenberg said.
"Meaning that they need a vast amount of ammunition, spare parts and also maintenance."
Some of the fiercest fighting is currently focused around the eastern town of Bakhmut, which Russian forces have been attempting to capture for months.
The United States says it expects to seeing fighting continue at a "reduced tempo" in the coming months as both sides look to reconstitute their forces.
Stoltenberg said he had "no more information" about alleged Ukrainian drone strikes on air bases inside Russia, after Washington insisted it had "neither encouraged nor enabled" any such attacks by Kyiv.
But the NATO chief insisted the fundamental issue remained that Ukraine was fighting to protect itself as Moscow bombards civilian infrastructure in a bid to cut people off from electricity and heating over the winter.
"Ukraine has the right to defend itself against these kinds of attacks," he said.
Stoltenberg said conditions for a peaceful resolution of the conflict "are not there now because Russia has shown no sign of engaging in, in negotiations, which are respecting the sovereignty and territorial integrity of Ukraine".