Ukraine's Western backers were set to focus on keeping ammunition flowing to the war-torn nation at a meeting on Tuesday, as Kyiv presses for fighter jets to push Russia back.
President Volodymyr Zelensky has knuckled down on his plea for Western aircraft after securing commitments for tanks, air defence and precision missiles.
But allies insist they are scrambling to ensure his forces have the ammunition they need on the ground to push back renewed Russian offensives.
"It is clear that we are in a race of logistics," NATO Secretary General Jens Stoltenberg said ahead of the meeting of the US-led Ukraine Defence Contact Group in Brussels.
"Key capabilities like ammunition, fuel, and spare parts must reach Ukraine before Russia can seize the initiative on the battlefield. Speed will save lives."
Ukraine's Western supporters -- spearheaded by the United States -- have already supplied billions of dollars of arms to help Kyiv hold back Moscow.
- 'More troops, more weapons'-
Now, just under a year into the war, Russian President Vladimir Putin is once again stepping up his brutal assaults in the east of the country.
"We see how they are sending in more troops, more weapons, more capabilities to try to pressure the Ukrainians," Stoltenberg said.
The fighting is consuming vast quantities of ammunition, straining stockpiles and industries on both sides of the confrontation.
Stoltenberg warned that Kyiv's current rate of expenditure was "many times higher" than the output in NATO countries.
Allies continue to raid their shelves for the rounds -- especially 155-millimetre shells -- that Ukraine is firing by the thousands each day.
NATO is scrambling to get its factories to pump out more, and allies are eyeing plans for joint weapons purchases, higher defence spending and longer-term contracts.
Estonian Prime Minister Kaja Kallas has called on EU states to acquire arms for Ukraine together, in the same way the bloc bought Covid-19 vaccines in bulk.
- 'Make a difference' -
Zelensky issued a powerful call during a trip to London, Paris and Brussels last week for NATO members to send fighter planes and longer-range missiles.
The Ukrainian leader won a commitment to train pilots from Britain, but did not get any firm promises that his forces will get Western planes.
Slovakia has said it is willing to discuss sending Soviet MIG-29 planes to help replace losses to Ukraine's current stocks.
Diplomats from several NATO allies said they did not expect any firm announcement from Tuesday's meeting on supplying Western jets, but that momentum was building.
The United States -- by far the biggest supplier of arms to Ukraine -- is seen as key as it could greenlight sending the widely used F-16 fighters.
Stoltenberg pointed out that over the year of war the support from the West has already "evolved" from anti-tank weapons to advanced Patriot air defence systems.
"Regardless of what you think about aircraft, that will take time," Stoltenberg said.
He urged allies to make good on the promises of fighting vehicles and tanks they have announced.
"We need to now at least ensure that we deliver what we can deliver in the short term, because that can really make a difference on the battlefield in the coming weeks," he said.