'We will not waver': Biden highlights unity on Ukraine as high-stakes NATO summit ends

President Joe Biden highlighted allied unity in a major speech Wednesday following a two-day, high-stakes NATO summit in Vilnius, Lithuania.

Biden spoke to a large crowd gathered in the courtyard at Vilnius University, where he touted the strength of the alliance and the importance of continued support for Ukraine against Russian invaders.

"Today, our alliance remains a bulwark of global security and stability as it's been for more than seven decades," Biden said.

"NATO is stronger, more energized, and yes, more united than ever in its history," he continued. "Indeed, more vital to our shared future. It didn't happen by accident."

Biden said Russian President Vladimir Putin thought the alliance would fracture, but instead the U.S. has built a coalition of more than 50 nations to support Ukraine's sovereignty.

“We will not waver," Biden said. "I mean that. Our commitment to Ukraine will not weaken. We will stand for liberty and freedom today and tomorrow and for as long as it takes."

Biden emphasized an attack on one allied nation is an attack on all as he vowed NATO would always defend its people and territory.

"The defense of freedom is not the work of a day or a year," Biden said. "It's the calling of our lifetime; of all time. We are steeled for the struggle ahead. Our unity will not falter, I promise you."

All eyes were on Biden earlier Wednesday as he met with Ukrainian President Volodymyr Zelenskyy. The Ukrainian leader said he had a "good, powerful" discussion with Biden that ran twice as long as scheduled.

Despite his earlier harsh tone over the lack of a clear timeline for Ukraine to join the alliance, Zelenskyy said he felt satisfied with the outcome of the summit as he sat alongside Biden.

"We have great unity from our leaders and security guarantees, that is a success for this summit, I think so, but it's my opinion," Zelenskyy said.

The U.S. and global allies unveiled new security commitments for Ukraine, and reassured Kyiv has a place in the treaty organization after the war is over and after certain reforms are implemented.

Zelenskyy also singled out the aid provided by the U.S., thanking Biden for his decision last week to send controversial cluster munitions to Ukraine as it continues its counteroffensive against Russia.

Biden praised Zelenskyy and Ukraine for their "resilience and resolve" and said he looks forward to the day they can celebrate their official entry into NATO.

When ABC News asked Zelenskyy how soon Ukraine would like to join the alliance after the conflict ends, Biden offered a sarcastic response of "an hour and 20 minutes."

Biden secured a major foreign policy win earlier this week when Turkey agreed to back Sweden's bid to join the alliance, a sudden reversal more than a year after the Nordic nation applied for membership.

The president strongly pushed for Sweden's entry, and lauded the agreement reached between Prime Minister Ulf Kristersson and Turkey's President Recep Tayyip Erdogan on the eve of the summit. Questions have been raised about how much of a role the U.S. played in the agreement, as the administration announced Tuesday it is moving ahead with the potential sale of American F-16 fighter jets to Ankara.

Following his speech in Lithuania's capital, Biden will travel to Helsinki, Finland for a U.S.-Nordic Leaders Summit. There, he will celebrate Finland becoming the newest member of the NATO alliance.

ABC News' Justin Gomez and Cheyenne Haslett contributed to this report.