NATO leaders have agreed that Ukraine's future lies within their alliance, but they have hesitated to spell out when that might happen. Now, they say they will extend an invitation when "conditions are met."

On Tuesday, President Volodymyr Zelenskyy traveled to the Lithuanian capital of Vilnius to meet with NATO leaders at their annual summit. He wants Ukraine to join as soon as possible after the war ends.

Zelenskyy, addressing a crowd that welcomed him with Ukrainian flags, said, "Ukraine will make NATO stronger."

He had earlier criticized the leaders for not providing a timeframe, which he called "absurd."

NATO members released a communique on Tuesday. They had struggled to agree on the wording, and they say they will need to carry out periodic reviews to ensure Ukraine meets their standards on democracy and security.

Still, they have opened a fast-track by dropping some requirements for membership.

NATO Secretary General Jens Stoltenberg said, "There has never been a stronger message from NATO at any time, both when it comes to political message on the path forward for membership and the concrete support from NATO allies."

Stoltenberg added that NATO allies have never provided timelines for admitting new members. He said the process is -- and always has been -- based on meeting conditions.