According to US and European officials, NATO countries are hurrying to establish a plan to give long-term support to Ukraine, but are grappling with how to best ensure the country’s security until it can join the armed alliance.

With four weeks until a NATO summit in Vilnius expected to approve the plan, there is agreement that Ukraine cannot join the alliance while fighting against Russian forces continues, a position accepted in early June by President Volodymyr Zelenskiy after months of pleading for quick admission.

Alliance members are close to agreeing incremental steps to strengthen ties with Ukraine, including upgrading how NATO and Kyiv cooperate and a multi-year program to help Ukraine bring its security forces to NATO operational and technical standards, according to officials.

The allies have yet to resolve differences over how to address Ukraine’s desire for membership, which has been governed by a vague 2008 declaration that it will join the North Atlantic Treaty Organization without setting out how or when.

U.S. ambassador to NATO Julianne Smith told reporters on Wednesday that members are still discussing how to respond to the Kyiv government’s membership aspirations.

“There’s a rich conversation going on across the alliance with a whole array of views,” said Smith.

A senior alliance source, speaking on condition of anonymity, said there is “a hard search on to find a mechanism that brings Ukraine closer to NATO without taking them into NATO.”

Western governments such as the U.S. and Germany are wary of moves they fear could take the alliance closer to entering an active war with Russia, which has long seen NATO’s expansion into eastern Europe as evidence of Western hostility.

Asked on June 2 about Ukraine’s aspirations to join NATO, Kremlin spokesman Dmitry Peskov said it “would be a potential problem for many, many years.”

Russian President Vladimir Putin sent his forces into Ukraine in February last year saying Russian security had to be protected. Few military analysts expect Ukraine’s just-launched counteroffensive to bring the grinding conflict to a quick end – instead, many predict years of fighting.

Over that time, popular support for defending Ukraine in the West might fade and the 2024 U.S. election could yield an administration less willing to spend money on the war.