White House National Security Advisor Jake Sullivan said the summit will underscore NATO's readiness to consider Ukraine's membership, which he called a "milestone" in itself.

"The NATO Summit will dive into the question of NATO's relationship with Ukraine, both the question of its pathway towards future membership and the question of an ongoing partnership that has existed for several years," Sullivan said.

But "Ukraine will not be joining NATO coming out of this summit," he said.

Kyiv "still has further steps that it needs to take before membership," Sullivan added.

"Ukraine will have the opportunity to discuss the reforms that are still necessary for Ukraine to come up to NATO standards."

Ukrainian President Volodymyr Zelensky is set to attend the two-day gathering in Lithuania to make the case that his country should join when Russia's war ends.

Sullivan also said that the White House expects Sweden's NATO membership to win final approval in the near future.

Sullivan said it was "possible" that Turkey and Hungary will drop their opposition at next week's summit.

If not, "we believe it will happen in the not-too-distant future."

Sullivan said there was "fundamentally goodwill" toward Sweden's bid within the alliance.

"A strong NATO makes the United States and the entire world more safe and more secure," he said.

Sweden and Finland dropped decades of military non-alignment and applied to join NATO last year in the wake of Russia's invasion of Ukraine.

Finland formally joined the bloc in April, but, empowered by the rule that requires unanimous support for a new member, Sweden's entrance was blocked by Turkey and Hungary.

Turkish President Recep Tayyip Erdogan is holding up Sweden's entry because of a longstanding dispute about Stockholm's permitting alleged Kurdish militants to live in the Nordic country.