The official, Andriy Yermak, said the failure of the alliance to deliver a “strong” decision at the July 11-12 summit would demoralise Ukrainians and that it had demonstrated it was ready to join with its fighting on the battlefield.
“We expect that Ukraine will be invited to NATO with an open date,” Yermak told a webinar held by the Atlantic Council think tank.
“This can create a signal,” he said.
President Volodymyr Zelenskiy has pressed hard for Ukrainian membership of the military alliance but also said he recognises it would be impossible to join while Russia’s war in Ukraine is still raging.
Yermak said that consultations were ongoing between the United States and Ukraine on measures that NATO leaders would approve in Lithuania to bolster Ukraine’s security until it receives the alliance’s collective security guarantee.
Ukraine’s allies are divided over how fast the country should join and some NATO members are wary of any move that might take the alliance closer to war with Russia.
Ukrainian forces have gone on the counteroffensive in the southeast in a bid to recapture swathes of occupied land that Russia has heavily fortified.
President Vladimir Putin said on Wednesday that Russia had seen a “lull” in Ukraine’s counteroffensive and that Ukrainian forces had suffered heavy losses in attacks in the south.
His comments came as Zelenskiy said his army’s progress was “slower than desired” but that Ukraine would not be pressured into rushing it.
Putin has begun speaking with increasing frequency about the battlefield situation, perhaps reflecting the fact that the 16-month-old war has reached a critical moment with the launch of Ukraine’s long-expected push.
“Oddly enough, at the moment we are seeing a certain lull. This is due to the fact that the enemy is suffering serious losses, both in personnel and equipment,” he said.
But he said that Ukraine’s offensive potential “has not yet been exhausted, there are also reserves that the enemy is thinking about where and how to introduce”.
For the second time in less than a week, he said that the Ukrainian forces had “no chance”.
The BBC quoted Zelenskiy as saying in an interview that the military push was not going easily because 200,000 square km of Ukrainian territory had been mined by Russian forces.
“Whatever some might want, including attempts to pressure us, with all due respect, we will advance on the battlefield the way we deem best,” he added.
Ukraine says it has reclaimed eight villages so far in its counteroffensive although only one of these was in the past week.