Ukrainian President Volodymyr Zelenskyy was critical of the NATO allies Tuesday as they sat down for a summit still unsure how to advance Kyiv's membership bid.

Zelenskyy, who was expected in Vilnius during the two-day summit, denounced as "absurd" the reluctance of some NATO leaders to provide a clear timetable for Ukraine to join the alliance.

"Uncertainty is weakness. And I will openly discuss this at the summit," Zelenskyy tweeted.

The alliance backs Ukraine in its battle against Russia's 16-month-old invasion, but several members – notably U.S. President Joe Biden – oppose giving Ukraine a timetable for membership.

Instead, the Vilnius summit is expected to produce more commitments on arms shipments and a reaffirmation that Ukraine's eventual place is within the alliance once the war is won.

Germany's Chancellor Olaf Scholz said that the G-7 group of major industrialized economies would offer a package of support to kick in once "peace is obtained."

Russian 'terror'

Arriving at the talks, President Emmanuel Macron said France would join Britain in supplying long-range cruise missiles to allow Ukraine to strike Russian targets in depth.

But all this is unlikely to appease Zelenskyy whose forces have launched a counteroffensive to reclaim Russian-occupied territory at a cost of accelerating casualties.

"It seems there is no readiness neither to invite Ukraine to NATO nor to make it a member of the alliance," he said, citing "signals that certain wording is being discussed without Ukraine."

"This means that a window of opportunity is being left to bargain Ukraine's membership in NATO in negotiations with Russia. And for Russia, this means the motivation to continue its terror."

But if Russia was encouraged by the tenor of the debate in Vilnius, it did not say so, instead denouncing what it dubbed "the strong anti-Russian character" of the meeting.

Kremlin spokesman Dmitry Peskov warned that Russia's security could be jeopardized by Sweden's imminent arrival in the alliance, and warned France over the delivery of SCALP missiles.

"From our point of view, this decision is a mistake with consequences for the Ukrainian side, because this will of course force us to take countermeasures," Peskov said.

The fury emanating from Moscow and Kyiv stood in stark contrast to the message to Ukraine from NATO Secretary General Jens Stoltenberg, buoyed by Türkiye's decision to lift a veto on Sweden's membership.

"We will send a clear message, a positive message on the path forward. The text in the communique will be made public within hours," he declared.

German Patriot missile systems and French fighter jets were guarding the skies as the NATO leaders gathered in the Lithuanian capital.

No timetable

While eastern European nations have pushed for an explicit timetable to allow Kyiv to join, the U.S. and Germany are reluctant to go beyond an earlier vow that it will become a member one day.

Biden, who will meet Zelenskyy on Wednesday, has said there is no agreement to offer Kyiv membership while the war with Russia rages, as this could drag NATO directly into the conflict.

White House National Security Advisor Jake Sullivan told reporters NATO will draw up a path of reforms that Ukraine will need to undertake, but without giving a "timetable."

The U.S., Britain, France and Germany have been negotiating over long-term commitments on weapons supplies to reassure Kyiv before it joins NATO.

These fall far short of Zelenskyy's desire to be under the alliance's collective defense umbrella but could reassure him that his nation can keep on resisting.

Drawing up something similar to the U.S. arrangement with Israel – which sees Washington sending $3.8 billion (3.5 billion euros) of weapons each year for a decade – is one possibility.

Lithuania's President Gitanas Nauseda insisted only NATO's article five mutual defense clause "can provide real security guarantees which would deter Russia from any future aggression."

In a reminder of the daily threat facing Ukrainians, Russia targeted Kyiv and the port city of Odesa in yet another overnight drone attack. There was no immediate information on casualties.

NATO overhaul

The biggest war in Europe since World War II has propelled NATO into the most sweeping overhaul of its defenses since the end of the Cold War.

Alliance leaders should sign off on new regional plans to protect against any potential Russian attack and agree to bolster defense spending targets.

"On our side of the fence, we have to up the game of preparedness and just keep our eyes open," Latvian Prime Minister Krisjanis Karins said.

But letting Ukraine in remains a step too far for some for now.

Diplomats have been wrangling up to the wire over the exact wording of the final communique as they seek to convince Ukraine it is moving forward.

In 2008, NATO left Ukraine in a grey zone by vowing it will become a member but failing to back that up with any concrete progress.

Kyiv's push to join the Western bloc enraged Putin and was used as a pretext to justify his war.