Ukrainian President Volodymyr Zelensky has called on NATO to resolve the issue of Ukraine and Sweden's membership bids, saying indecision is threatening the strength of the alliance and global security.
Battling a Russian invasion for more than 16 months, Kyiv has expressed increasing frustration with its Western allies over guarantees that it will one day join the alliance.
Mr Zelensky spoke on a visit to Slovakia before he is due to head to Turkey for talks with President Recep Tayyip Erdogan, who has stalled Sweden's membership bid to NATO.
"I think there is not enough unity on this. This is a threat to the strength of the alliance," the Ukrainian leader said.
"This is very important for the security of the whole world."
President Zelensky said that Ukraine expected "positive results or at least some steps towards the positive outcome" at a NATO summit in Lithuania next week.
"I believe that the situation with the aggressor, with Russia, depends on this.
"Because Russia is counting on the world to show weakness and disunity in the alliance, and this cannot be allowed."
President Zelensky also said that he expects "defence packages" at the summit "and not just promises, but with clear deadlines".
NATO Secretary-General Jens Stoltenberg reaffirmed his view that Ukraine would become a member.
"Our summit will send a clear message: NATO stands united, and Russia's aggression will not pay," Mr Stoltenberg told a news conference in Brussels.
Mr Zelensky arrived in Slovakia, Ukraine's western neighbour, from the Czech Republic and will travel to Turkey for talks with President Erdogan later today.
The Istanbul meeting come on the eve of the 500th day since Russia's invasion.
The talks with Mr Erdogan - an important broker in the conflict - are to focus on an expiring deal to ship Ukrainian grain across the Black Sea, as well as next week's NATO summit.
Speaking ahead of President Zelensky's visit, the Turkish leader appeared to leave open the possibility of backing Sweden's NATO candidacy, saying his country would "make the best decision, whatever it is" at the upcoming summit.
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President Erdogan is blocking the candidacy because of a longstanding dispute about Stockholm's perceived lax attitude toward alleged Kurdish militants living in the Nordic country.
Turkey's resistance to accepting Sweden into the alliance has irritated the United States and the European Union, which argue that Sweden has done enough to address Turkey's concerns.
Mr Erdogan reaffirmed those concerns today, but he did not rule out the possibility of giving his green light to Sweden's membership, which he will discuss with Swedish Prime Minister Ulf Kristersson on Monday at NATO-organised talks.
Both the Ukrainian and Turkish leaders want to extend a United Nations and Turkey-brokered deal with Russia under which Ukraine has been allowed to ship grain to global markets during the war.
The agreement will expire on 17 July unless Russia accepts its renewal.
Mr Erdogan has tried to leverage good working relations with both Mr Zelensky and Russian President Vladimir Putin to mediate an end to the war.
Turkey staged two early rounds of peace negotiations and is pushing for more talks.
Before visiting the Czech Republic yesterday, Mr Zelensky travelled to Sofia to discuss weapons deliveries with Bulgaria, a major supporter and ammunition producer.
The Kremlin criticised the visit to Bulgaria, saying the Ukrainian leader was trying to "drag" other countries into the war.
