NATO leaders said Tuesday they "will be in a position" to invite Ukraine to join the alliance when allies agree and "conditions are met."

"Ukraine's future is in NATO," leaders said in a news release, adding that the alliance will support Ukraine in making reforms on its path toward membership.

Although many NATO members have funneled arms and ammunition to Ukrainian President Volodymyr Zelenskyy's forces, there is no consensus among the 31 allies for admitting Ukraine into NATO's ranks. There have been sharp divisions within the alliance over Ukraine's desire to join, which was promised back in 2008 even though few steps were taken toward that goal.  

"We reaffirmed Ukraine will become a member of NATO and agreed to remove the requirement for a membership action plan," NATO Secretary-General Jens Stoltenberg told reporters Tuesday, referring to a key step in joining the alliance.

"This will change Ukraine's membership path from a two-step path to a one-step path," he said.

NATO membership would afford Ukraine protection against Russia, a giant neighbor that annexed its Crimean Peninsula almost a decade ago and more recently seized vast swaths of land in the east and south. Joining NATO would also oblige Kyiv to reform its security institutions, improve governance and curb corruption -— work that would also ease the country's path into the European Union.  

"It's unprecedented and absurd when a time frame is set neither for the invitation nor for Ukraine's membership," Zelenskyy tweeted as he headed to the NATO summit in Vilnius. "While at the same time, vague wording about 'conditions' is added even for inviting Ukraine. It seems there is no readiness to invite Ukraine to NATO or to make it a member of the Alliance."

Asked about Zelenskyy's concerns, Stoltenberg said the most important thing now is to ensure that his country wins the war, because "unless Ukraine prevails there is no membership to be discussed at all."

The broadside from Zelenskyy could renew tensions at the summit shortly after it saw a burst of goodwill following an agreement by Turkey to advance Sweden's bid to join NATO. Allies hope to resolve the seesawing negotiations and create a clear plan for the alliance and its support for Ukraine.

"We value our allies," Zelenskyy wrote on Twitter, adding that "Ukraine also deserves respect." He also said: "Uncertainty is weakness. And I will openly discuss this at the summit."

Zelenskyy is expected to meet Wednesday with President Biden and other NATO leaders. 

The Biden administration supports NATO's "open door" policy, welcoming membership when Ukraine is ready and with unanimous agreement from allies, U.S. Secretary of State Antony Blinken told "CBS Mornings" on Tuesday.

Blinken said Ukraine has made "good progress" in the direction of membership but said "they have more work to do," like continuing to reform their military and deepen democratic reforms.

"The bottom line is this: here in Vilnius, a really robust package of support for Ukraine, political support, practical support and further progress down the road toward membership in NATO," said Blinken.

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