WASHINGTON (AP) — Ukraine is on an "irreversible" path to NATO membership, U.S. and European officials said Wednesday, advancing assurances from allies that it will be allowed to join the Western military coalition after its war with Russia ends.

In another boost for Ukraine, the U.S., the Netherlands and Denmark announced Wednesday that the first NATO-provided F-16s were on their way to Ukraine and would be flying this summer following months of work. Ukrainian President Volodymyr Zelenskyy tweeted his appreciation on the effort to strengthen his air force, coming after Ukraine saw one of the deadliest strikes of the war.

U.S. Secretary of State Antony Blinken, Czech President Petr Pavel, Finnish President Alexander Stubb and Belgian Prime Minister Alexander De Croo all used the word "irreversible" to describe the way forward for Ukraine as NATO leaders gathered for a summit in Washington.

Stubb and Latvian President Edgars Rinkevics both said the language was expected in the final summit declaration from all 32 NATO allies.

"I think it's very important to give a message to the Kremlin from here — that Ukraine's path and bridge towards NATO membership is now irreversible," Stubb told reporters as he arrived at the summit.

Zelenskyy, fearing his country would otherwise be left to fight a stronger Russia indefinitely, has battled for at least a firm guarantee from NATO that Ukraine can join the military alliance.

The U.S. and some other countries have opposed membership for Ukraine while the conflict with Russia continues to avoid an escalation of tensions with Russia that could lead to a larger war. They also have stressed that Ukraine must take significant steps to address corruption as well as other systemic reforms.

Russian President Vladimir Putin has long bitterly opposed neighboring Ukraine's fight to join the Western alliance, declaring it an encroachment on Russia's security and interests.

NATO Secretary-General Jens Stoltenberg underlined that Ukraine will not join the alliance's ranks immediately. But he insisted that must happen after the war is over to ensure that Russia never attacks it again.

"I strongly believe that when the fighting stops, we need to ensure that Ukraine has the capabilities to deter future aggression from Russia, and they need security guarantees," Stoltenberg said.

Zelenskyy, in Washington for the NATO summit, had stressed what he called Ukraine's urgent need for the F-16 fighter jets in a speech to friendly Republican lawmakers Tuesday night. He said his country needed more than 100 to be able to start to counter the devastating Russian air attacks on Ukraine's cities, energy infrastructure and other vital targets. He said Russia was using 300 jets to carry out the attacks.

In post on X, Zelenskyy thanked the three countries "for taking practical steps to achieve the goal of all Ukrainians: to strengthen the Ukrainian air force with F-16s." The first flight-ready jets were being transferred by the Netherlands and Denmark, and the White House said they would be "flying operational" this summer. Zelenskyy also thanked Belgium and Norway for their commitment to send the jets.

European and U.S. allies have announced other new arms deliveries, such as dozens of air defense systems, including Patriots, at the NATO summit. Opposition from Republican lawmakers allied to former President Donald Trump blocked a U.S. support package to Ukraine for months earlier this year, allowing Russia to make battlefield gains against Ukrainian forces who were fighting with dwindling arms and ammunition.

Europeans and NATO, as a lesson from that setback, have vowed to take on more of the responsibility for ensuring a reliable flow of military support to Ukraine.

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Cook reported from Brussels. Matthew Lee in Washington contributed.