President Volodymyr Zelenskyy of Ukraine intends to make a surprise visit to Washington on Wednesday, the first time the leader has left his war-torn country since Russia invaded 10 months ago.

Zelenskyy’s plans to address a joint session of Congress and at the White House as the Biden administration plans to announce the delivery of a Patriot missile battle system to help Ukraine with its air defenses, according to two people familiar with the plans but not authorized to publicly discuss them because of security concerns.

The trip is not certain to happen, the people cautioned. Zelenskyy was still in Ukraine on Tuesday evening, and there are concerns about his ability to leave his country and then return again.

His visit to Washington would come as Congress is on the verge of passing another $45 billion in assistance to Kyiv in the year-end omnibus bill, which would bring the total to over $100 billion in emergency aid from the United States.

News of Zelenskyy’s planned trip was first reported by Punchbowl News.

The White House pushed Congress to include substantial Ukraine aid in the bill, facing an imminent Republican majority in the House that seems to be less inclined to fund the embattled country. If passed, it would bring the total to over $100 billion in emergency aid from the United States.

Zelenskyy would likely meet with congressional leaders and national security committee chiefs, and could address a joint session of Congress. In a short letter to colleagues, House Speaker Nancy Pelosi urged members to be physically present Wednesday night for a “very special session” with a “very special focus on Democracy.”

Earlier Tuesday, Zelenskyy, who travels with heavy security, was in Bakhmut, a city in eastern Ukraine that has come under heavy Russian artillery attacks. The Ukrainian president hasn’t made a trip overseas since Russia invaded his country in February, though he has addressed Congress and other world capitals virtually.

“This week is extremely important for Ukraine — in order to get through this winter and next year,” Zelenskyy said Tuesday from his home country. “Our fighters gave me our flag today and asked to pass it on to those whose decisions are very important for Ukraine, for all our warriors. We will definitely do it. We will definitely endure. We will definitely get the necessary support for Ukraine!”

Russian President Vladimir Putin visited Belarus on Monday, prompting concerns that the Russian ally could join in the ground war against Ukraine. The Russian military has suffered heavy losses in the invasion but the Kremlin has shown no signs of abandoning its war.

The Pentagon has ramped up preparations to arm Kyiv, finalizing plans to send the Patriot missile defense system, which should greatly enhance Ukraine’s ability to defend itself against attacks from the skies, including missiles and armed drones.

White House aides have privately admitted for months that, at a certain point, congressional funding for the war would slow as it drifts from the headlines. But there is a push by the administration to make sure Ukraine has the assistance it needs to make it through the winter, despite Russian attacks on the electrical grid that have plunged much of the nation into the darkness and left millions of war-weary residents without heat or light.

Biden has yet to visit Kyiv, due to significant security concerns. But he and Zelenskyy have talked frequently and the American president has made supporting UkraineKyiv a central focus on his administration.

Ukraine’s counteroffensive, so successful when launched in late summer, has stalled along both the southern and eastern fronts, allowing Russian forces to dig in. The cold winter has slowed the fighting — which has devolved into World War I-style trench warfare — but Ukrainian military officials this week warned that recent Russian troop and tank movements could telegraph another major assault in the weeks ahead, perhaps even toward Kyiv, the capital.

His war machine stalled and humbled, Putin has turned to long-range strikes and drones to destroy half of Ukraine’s energy infrastructure, causing regular blackouts and power cuts for millions. As temperatures drop dangerously, more Ukrainians may opt to flee the country, seeking shelter in neighboring nations and further straining the economies of other European nations.

To this point in the war, Biden has received high marks for reviving NATO and holding together a transatlantic alliance to stand against Putin. Senior White House aides have been impressed with European unity to this point. But they know that Biden’s job will grow more challenging during these next few difficult months.

Biden has led Western leaders in pledging to support Ukraine “for as long as it takes.” But an energy crisis across Europe has forced significant cutbacks and the continent — where inflation stands at 11 percent — could be on the brink of a recession.

Zoya Sheftalovich contributed to this report.