"Ukraine has urgent needs," Stoltenberg said as NATO foreign ministers met in Brussels. "Any delay in providing support has consequences on the battlefield as we speak. So we need to shift the dynamics of our support."

"We must ensure reliable and predictable security assistance to Ukraine for the long haul so that we rely less on the voluntary contributions and more on NATO commitments, less on short-term offers and more on multi-year pledges."

Diplomats and officials have said that Stoltenberg has proposed creating a 100-billion-euro ($108 billion) fund to help arm Ukraine in its fight with Russia.

"Moscow needs to understand that they cannot achieve their goals on the battlefield and they cannot wait us out," Stoltenberg said, without giving details of his proposal.

Foreign ministers were to hold preliminary talks on the five-year plan during a two-day meeting as NATO pushes to forge a package of support for Ukraine by a July summit in Washington.

Diplomats caution that there are many questions on where financing would come from and that the proposal could change dramatically by the summit.

The plan from Stoltenberg would also see NATO taking more control of coordinating arms supplies to Kyiv from a US-led grouping that currently helps oversee support.

Officials say that could help insulate the flow of weaponry to Ukraine from a potential return of Donald Trump to the White House in November.

The move would mark a major shift for the Western military alliance which has so far refused as an organisation to send weapons to Ukraine for fear it would drag NATO closer to a conflict with Russia.

Latvian foreign minister Krisjanis Karins called the 100-billion-euro fund "a very good proposal".

"This is the direction that we need to think of, how we can pool our common resources to be more effective in aiding Ukraine," he said.

But Hungary -- one of the friendliest countries to Russia in NATO -- said it would not support any proposal that might "draw the alliance closer to war".

Stoltenberg's proposal comes as Ukraine's outgunned forces are struggling to hold back Russia in the face of dwindling supplies from Kyiv's Western backers.

A $60-billion US funding package is currently stalled in Congress but there are hopes lawmakers could move to pass it in the coming weeks.