WASHINGTON -- Ukrainian President Volodymyr Zelenskyy, bolstered by the planned presence of key European allies, will meet President Donald Trump at the White House on August 18 in a session that could go a long way to deciding his embattled nation's future.

One of the key items on Zelenskyy's agenda in the meeting -- due to begin at 1:10 p.m. in the Oval Office -- is securing solid security guarantees from the US leader against further Russian aggression, something US leaders say is a real possibility after months of downplaying the potential.

Steve Witkoff, an envoy widely regarded as one of the key US negotiators with Moscow, suggested that Trump and Russian President Vladimir Putin have agreed to provide robust security guarantees for Ukraine.

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We were able to win the following concession [from Putin]: That the United States could offer Article 5-like protection, which is one of the real reasons why Ukraine wants to be in NATO," Witkoff told CNN's State of the Union program.

It was the first time we had ever heard the Russians agree to that, added Witkoff, calling it game-changing.

Zelenskyy -- who has long expressed desires to join NATO or to receive meaningful security guarantees from Washington and Europe's so-called "Coalition of the Willing" -- said the issue will be upfront when he meets with Trump.

There are no details how it will work, and what Americas role will be, Europes role will be, and what the EU can do and this is our main task: We need security to work in practice like Article 5 of NATO, he said, referring to the alliance's clause that states an attack on one member is considered an attack on all.

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US officials have long rejected Kyiv's membership in NATO and have been reticent in the past to speak of direct security guarantees for Ukraine. Administration officials said any guarantees would be outside of NATO.

"European leaders have three key goals...to pin down more details on possible US security guarantees for Ukraine; to work on preparations for a possible trilateral meeting between Presidents Vladimir Putin, Volodymyr Zelenskyy, and Donald Trump, and to push back on the idea of land swaps, Eurasia Group said in a note.

The White House meeting is coming after Trump met with Putin in an Alaska summit that appeared to yield little if any results but worried Kyiv and its allies over what critics perceived as a tilt by Trump back toward the Kremlin leaders position on ending the war.

Most alarming to Ukraine and its supporters have been Trumps remarks that Kyiv will have to cede territory to Russia in a "land swap," something Ukraine has long rejected.

Also concerning were Trumps comments that an immediate cease-fire -- long advocated by Washington, Kyiv, and European leaders -- was no longer the desired next step.

Instead, Trump seemingly in line with Putins wishes said the sides should negotiate toward a full peace deal, which would likely take much longer and, critics say, buy Russia time to score further battlefield gains against the outmanned and outgunned Ukrainian defenders.

European leaders, many of whom held a video conference on August 17 to discuss the Ukraine war, said they will travel to Washington to support Zelenskyy during his meeting with Trump, although it was not immediately clear which sessions they would participate in.

"I will join the meeting with President Trump and other European leaders at the White House tomorrow," European Commission PresidentUrsula von der Leyensaid.

Following von der Leyens statement, a stream of European leaders, along with NATO Secretary-General Mark Rutte, also announced their plans to travel to Washington.

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French President Emmanuel Macron, British Prime Minister Keir Starmer, German Chancellor Friedrich Merz, Italian Prime Minister Giorgia Meloni, and Finnish President Alexander Stubb, are expected to join.

Our goal for tomorrows talks is to present a united front between Ukraine and its European allies, Macron said.

"Do I think President Putin wants peace? The answer is no," Macron said following the video conference with fellow European leaders.

"I believe he wants Ukraine's capitulation," Macron added.

Macron and British Prime Minister Starmer, co-chairs of the "Coalition of the Willing" group, said in a joint statement that European leaders "commended President Trumps commitment to providing security guarantees to Ukraine, in which the Coalition of the Willing will play a vital role through the Multinational Force Ukraine, among other measures."

Thestatementreiterated Europe's "readiness to deploy a reassurance force once hostilities have ceased, and to help secure Ukraines skies and seas and regenerate Ukraines armed forces."

Some in the administration on August 17 played down Trump's comments about bypassing an immediate cease-fire.

US Secretary of State Marco Rubio, in comments to NBC's "Meet the Press" program, insisted that an immediate cease-fire is "not off the table."

"I think what the president said...it was agreed to by all that the best way to end this conflict is through a full peace deal."

"Theres no doubt about that...Now, whether there needs to be a cease-fire on the way there, well, weve advocated for that. Unfortunately, the Russians as of now have not agreed to that."

US Secretary of State Marco Rubio: Cease-fire "not off the table."

Rubio told CBS that the details of the negotiations to end the war must be decided by the two belligerents, not by Washington.

The United States is not in a position to accept anything or reject anything, because ultimately, its up to the Ukrainians. Theyre the ones that Russia has to make peace with, Ukraine with Russia, Rubio said.