"The war in Ukraine is consuming an enormous amount of munitions, and depleting allied stockpiles," Stoltenberg told journalists.

"The current rate of Ukraine's ammunition expenditure is many times higher than our current rate of production. This puts our defence industries under strain."

Stoltenberg admitted that NATO was facing a "problem" as current waiting times for large-calibre ammunition have grown from 12 to 28 months.

But he insisted he was confident steps taken so far meant NATO members were "on the path that will enable us both to continue to support Ukraine, but also to replenish our own stocks".

Ukraine's Western backers -- who have supplied billions of dollars of arms -- will meet Tuesday to discuss Kyiv's weapons demands as Stoltenberg said Russian President Vladimir Putin is "launching new offensives".

The NATO chief said there was an ongoing discussion among allies about Ukraine's demands for modern fighter jets to be sent to the battlefield.

But he said a key focus was on making sure the necessary amounts of weaponry flowed to Kyiv's forces on time and that allies made good on commitments already made.

"It is clear that we are in a race of logistics," Stoltenberg said.

"Key capabilities like ammunition, fuel, and spare parts must reach Ukraine before Russia can seize the initiative on the battlefield. Speed will save lives."