Washington — President Biden and Group of 7 leaders announced Wednesday they are launching a long-term joint declaration of support for Ukraine aimed at helping the country bolster its military to defend itself from Russia's aggression and deter future threats.

"We're going to help Ukraine build a strong, capable defense across land, air and sea, from which they'll be a force of stability in the region and deter against any and all threats," Mr. Biden said in brief remarks alongside fellow G7 leaders and Ukrainian President Volodymyr Zelenskyy.

The president said the agreement makes it clear that support from Ukraine from the world's most powerful democracies "will last long into the future."

While the declaration includes members of the G7 — the U.S., Canada, France, Germany, Italy, Japan and the United Kingdom — it is open to other nations that wish to negotiate long-term bilateral security commitments with Ukraine, the leaders said.

"It's a powerful statement, a powerful statement of our commitment to Ukraine as it defends its freedom today ad as it rebuilds its future," Mr. Biden said. "We're going to be there as long as it takes."

After a bilateral meeting between Mr. Biden and Zelenskyy, the president told reporters that he hoped "we have finally put to bed the notion of whether or not Ukraine is welcome in NATO — it's going to happen. We're all moving in the right direction. I think it's just a matter of getting by the next few months."

Japanese Prime Minister Fumio Kishida stressed earlier that solidarity for Ukraine from the G7 "will never waver."

The declaration marks the start of talks with Kyiv to formalize through bilateral security commitments and arrangements long-term support for Ukraine. The framework aims to ensure Ukraine has a sustainable force capable of defending the country through continued security assistance and modern military equipment, strengthen Ukraine's economic stability through reconstruction and recovery efforts, and provide technical and financial support for Ukraine's needs stemming from Russia's ongoing war.

The announcement by the G7 leaders came on the final day of the NATO leaders summit in Vilnius, Lithuania, where one day earlier, the alliance declared that "Ukraine's future is in NATO." But the members declined to provide a timeline for when an invitation would be extended, saying only that would occur when Ukraine makes several reforms and allied countries "agree and conditions are met."

Zelenskyy was critical of the joint statement, saying in a tweet Tuesday that it was "unprecedented and absurd" that there was no defined timeframe regarding Ukraine's admittance to NATO. But on Wednesday, he acknowledged in a tweet that his country understands "that Ukraine cannot become a member of NATO while there is a war ongoing."

The outcome of NATO summit was a "much needed and meaningful success for Ukraine," Zelenskyy said in brief remarks alongside the G7 leaders.

"The Ukrainian delegation is bringing home a significant security victory for Ukraine, for our country, for our people, for our children," the Ukrainian president said. "It opens for us absolutely new security opportunities." 

In a speech before leaving Lithuania, Mr. Biden said the U.S. has "built a coalition of 50 nations to make sure Ukraine defends itself both now and is able to do it in the future as well." 

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

Mr. Biden said Russian President Vladimir Putin is making a bad bet that NATO's unity will break down as the war drags on, but said "our unity will not falter. I promise you." 

"The defense of freedom is not the work of a day or a year. It's the calling of our lifetime, of all time," he said. 

Amanda Sloat, senior director for Europe at the National Security Council, told reporters the announcement by the heads of the world's wealthiest nations is intended to help Ukraine build a powerful military.

"This process will ensure that the military assistance we provide Ukraine to defend itself against Russian aggression continues to be part of a long-term investment in Ukraine's future force," she said. "We'll focus on ensuring Ukraine has a sustainable fighting force capable of defending Ukraine now and deterring Russian aggression in the future."

Though Mr. Biden has repeatedly pledged that the U.S. will continue offering assistance to Ukraine, a number of Republicans in Congress, and some GOP candidates vying for the party's presidential nomination, have begun to question the need for more funding for Ukraine. 

But they face objections from senior Republicans, including Senate Minority Leader Mitch McConnell, who last month defended the security assistance that has gone to Ukraine.

"America's support for Ukraine has done much more than sustain their defense," he said in remarks on the Senate floor. "As I've said repeatedly, sending lethal western capabilities to the front lines has been a direct investment in America's own security in a number of concrete ways."