(CNN) -- Ukrainian President Volodymyr Zelensky is paying a dramatic visit to the US on Wednesday, using his first trip outside his homeland since it was invaded 300 days ago to rally his top international partner behind sustained military and economic assistance.
The trip, which US and Ukrainian officials arranged in secret over the past week, came with heavy risks. After arriving in Poland by train, Zelensky flew to Washington aboard an American military aircraft, US officials said. He arrived in the US shortly after midday, a source familiar with his travels told CNN. A separate source said he landed at Joint Base Andrews, just outside the nation's capital.
He will visit the Oval Office in the afternoon for extended talks with US President Joe Biden, who will announce he is sending nearly $2 billion in additional security assistance to Ukraine, including a sophisticated new air defense system. The two will convene a White House news conference before Zelensky addresses members of Congress on Capitol Hill in prime time.
The visit by the Ukrainian leader to Washington, expected to last only a matter of hours, amounts to a remarkable moment 10 months since Russia's war in Ukraine began.
"The President really believes that as we approach winter, as we enter ... a new phase in this war, of Mr. Putin's aggression, that this is a good time for the two leaders to sit down face to face and talk," said John Kirby, the strategic communications coordinator at the National Security Council, on "CNN This Morning."
Pulled together quickly by American and Ukrainian officials over the past 10 days, the wartime visit is meant to demonstrate in stirring fashion the continued American commitment to Ukraine at a moment when Biden's ability to maintain that support at home and abroad is being tested.
It will also provide an opportunity for Biden and top American officials to sound out Zelensky on how he views the trajectory of the conflict, and to offer their thoughts on what it would take to bring the war to an end.
"(Biden) will reinforce the fundamental message on this trip to President Zelensky directly -- to the Ukrainian people, the American people and the world publicly -- that the United States will stand with Ukraine for as long as it takes," a senior administration official said.
A surprise visit
Biden first discussed the prospect of Zelensky visiting Washington during a telephone call with the Ukrainian leader on December 11, an administration official said. A formal invitation was extended a week ago that Zelensky accepted, launching joint consultations on the security parameters of the risky, highly secretive trip.
Zelensky, who the official said was "very keen" to visit the US, determined those parameters met his needs, and the US set to work executing them. The trip was finally confirmed on Sunday.
"We are working in lockstep with him and his staff to make sure we can make this trip safely, both coming to the United States and coming back. We will continue to support his travel requirements as best we can," Kirby said.
Zelensky traveled to Poland by train as part of his journey to the United States on Wednesday. Video by CNN affiliate TVN in Poland captured the moment Zelensky arrived by train in Przemysl, near the Polish/Ukrainian border. Zelensky was then seen in a white 4x4 vehicle waiting to depart in a convoy.
Tight security has been enforced around Zelensky's visit amid concerns that Russia wants to incapacitate the Ukrainian president, a source close to the Ukrainian leader told CNN on Wednesday. According to the source, because of this ongoing threat, senior top government officials -- as well as embassy staff in the US -- were not informed about the schedule of the visit.
According to the source, the military risk had to be calculated allowing the Ukrainian president to make the short overseas trip without jeopardizing the military situation. Scheduling also had to be worked with the White House to assess availability for this to happen, the source added.
The source additionally told CNN that Zelensky did not want to travel had there not been a significant development in the bilateral relationship between Ukraine and the United States. Zelensky sees the US decision to send Patriot missile defense systems to Ukraine as a major shift in the relationship between the two allies.
When Zelensky arrives to the White House, he will meet for lengthy talks with Biden, along with key members of the US national security team. The official said Biden and Zelensky would engage in an "in-depth strategic discussion on the way ahead on the battlefield," along with the training and capabilities Western partners are providing Ukraine, the sanctions they have imposed on Russia and economic and energy assistance to the Ukrainian people.
The two men will also discuss what ending the war may take -- a sensitive conversation that US officials have insisted will not involve pressuring Zelensky to accept any concessions.
"I have no doubt they are going to talk about President Zelensky's notion of a 'just peace' and what that looks like, what are the components of that, and how do we help Ukraine get to that point," Kirby said.
"Mr. Putin is obviously not interested in diplomacy right now," he went on. "Quite the contrary. He's interested in killing more Ukrainian civilians."
Zelensky leaves Ukraine for first time since war began
Over the course of the 10-month invasion, Zelensky has emerged as the international personification of Ukrainian resistance and has spent much of the year appealing to nations for support. He has remained inside his country for the duration of the war, a reflection both of his desire to rally alongside his besieged country and the precarious security situation he would face outside Ukraine.
As the war nears its one-year anniversary, however, international support for Ukraine is being tested. Sanctions on Moscow have contributed to higher energy prices, particularly in Europe, which is heavily reliant on Russian oil and gas. In the United States, Republicans who are poised to take control of the House of Representatives have signaled they won't quickly approve massive new assistance packages for Ukraine.
On the battlefield, Ukraine has retaken key cities and shown unlikely resistance to an unprepared and ill-equipped Russian army. But Russian President Vladimir Putin has shown no indication he plans to ease up, and has been ruthless in targeting civilian energy infrastructure, lending a degree of misery to Ukraine's cold winter.
The timing appeared ripe for Zelensky to make a dramatic gesture like slipping out of Ukraine for the first time since the invasion began. For Biden, the visit presents an opportunity to reinforce his convictions for supporting Ukraine, even as the war plods on.
"We know that the days ahead, the conflict will continue," the senior administration official said. "The winter will be hard, and we will continue day-in, day-out to provide critical support to the Ukrainian people."
New military assistance includes crucial missile system
The new, $1.8 billion package Biden will unveil includes a Patriot surface-to-air missile system, which has been a longstanding request of Ukraine's to fend of Russian air attacks. CNN was first to report the US was expected to send the Patriot systems to Ukraine.
Unlike smaller air defense systems, Patriot missile batteries need much larger crews, requiring dozens of personnel to properly operate them. The training for Patriot missile batteries normally takes multiple months, a process the United States will now carry out under the pressure of near-daily aerial attacks from Russia.
The official said US troops would train Ukrainians to use the system in a third country. CNN has previously reported the training would occur at a US Army base in Grafenwoehr, Germany.
The system is widely considered one of the most capable long-range weapons to defend airspace against incoming ballistic and cruise missiles, as well as some aircraft. Because of its long-range and high-altitude capability, it can potentially shoot down Russian missiles and aircraft far from their intended targets inside Ukraine.
Russia has warned on unspecific "consequences" if the US provided Ukraine with Patriot missiles, viewing the shipments as further US engagement in the war. The official was clear, however, that Biden remained steadfast in keeping the United States out of direct conflict with Russia, despite the enhanced security assistance.
"The President has been very clear that we are going to lean forward and be robust in our support for Ukraine on the military, economic, energy and humanitarian fronts, but we are not seeking to engage in a direct war with Russia. And nothing about that will change tomorrow," the official said.
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