Nato Secretary General Jens Stoltenberg has put forward a proposal to establish a reported $100bn Nato fund over five years to give military aid to Ukraine, which would mark a significant milestone in the alliance’s support of Ukraine.

The proposal, which was unveiled at a two-day meeting of Nato foreign ministers on April 3-4 in Brussels to celebrate Nato's 75th anniversary, has had a mixed response, with the US in particular expressing some reservations, the Financial Times reported. The US has in the past resisted moves that could be seen as escalating the conflict or bringing Nato into direct confrontation with Russia.

Up to now voluntary Western support for Ukraine has been co-ordinated through the Ramstein group headed by the US but other Nato countries fear that a potential Donald Trump presidency next year could paralyse this approach, leaving Kyiv in the lurch. Stoltenberg's proposal would mean Nato members would make a multi-year pledge to help Ukraine, and give the alliance a co-ordinating role.

“For us, it is essential that we pour the ad hoc structures into reliable, long-term structures,” said German Foreign Minister Annalena Baerbock.

Stoltenberg's proposal envisages a collective fund comprising contributions from Nato member states, with the aim of providing financial assistance to Ukraine over the specified period. Stoltenberg has not commented on the size of the fund.

However, key details regarding the fund's accounting mechanics, including the incorporation of bilateral aid to Ukraine, remain subject to ongoing deliberations among alliance members. Some Nato members are worried about duplication, particularly with the EU's efforts.

Alliance leaders are expected to deliberate on the measure at their upcoming gathering in July. Individuals privy to the discussions, speaking anonymously to Bloomberg, revealed that the proposal is still under review and is likely to undergo modifications before securing approval from Nato's 30 members.

“Today we didn’t take any final decisions on what format we will establish, but we agreed to initiate planning,” Stoltenberg told reporters.

Hungary, which has often taken Moscow's side in Western discussions, also opposed the proposal.  Foreign Minister Peter Szijjarto said Budapest was opposed to “proposals that might draw the alliance closer to war or shift it from a defensive to an offensive coalition”.