President Biden defended the decision to send a Patriot missile defense system to Ukraine and denied the move was escalatory.

"It's a defensive system. It's a defensive weapon system. It's not escalatory, it's defensive," Biden said. "We'd love to not have them use it. Just stop the attacks," he said, referring to Russia.

Zelenskyy delicately added that he may call on the U.S. to send another Patriot missile in the near future, prompting laughter.

"We're working on it," Biden said with a smile.

Zelenskyy said, "We are in war. I'm sorry. I'm really sorry. That is my appreciation."

The training of Ukrainian troops on the Patriot missile battery could take "several months," according to a senior defense official who briefed reporters this afternoon.

"I can just say that the training will begin very soon," the official said, noting the "Ukrainians will have to complete the training in order to be able to field the system and it's the Ukrainians who are operating the system."

The Patriot missile system and JDAM kits to convert "dumb bombs" to "smart bombs" are included in the latest round of military aid to Ukraine. Ukraine has been asking for the advanced air defense system since shortly after Russia's invasion began.

The official would not provide any concrete timelines, telling reporters: "We also would obviously want to be really, really careful for operational security reasons to not you know, not be overly precise on a date, even once we have it."

-ABC News' Luis Martinez

Zelenskyy was asked by a reporter what his message is to the American people ahead of his address to U.S. lawmakers later this evening.

"I think I will tell you very simple things which are very important for me," Zelenskyy responded. "And I think so that we have the same values and the same understanding of the life, the sense of the life. My message: I wish you peace."

"And I wish you to see your children alive and adult," Zelenskyy continued. "And I wish you to see your children when they will go to universities, and to see their children. I think that is the main thing, what I can wish you."

Zelenskyy said the U.S. and Ukraine are fighting for "common victory against this tyranny" and predicted, "We will win."

"I really want win together," he said, before slightly amending his words: "Not 'want.' Sorry. I'm sure."

At the top of their joint news conference, Zelenskyy again thanked Biden, Congress and the American people for providing defense and aide to Ukraine against Russia, which he called a "terrorist country."

"This visit to the United States became really a historic one for our relations with the United States and the American leadership," Zelenskyy said.

"I have good news returning home," he continued, raising the new nearly $2 billion aid package. "This is a very important step to create a secure airspace for Ukraine, and that's the only way we would be able to deprive the terrorist country and terror attack."

Zelenskyy said "regardless of changes in the Congress," he believes there will be support for Ukraine, showing his apparent knowledge of resistance from House Republicans.

"We need to survive this winter, we need to protect our people, and we need to be very specific in this area. This is a key humanitarian issue for us right now. This is the survival issue," he said. "We are discussing sanctions and legal pressure on the terrorist country of Russia. Russia needs to be held accountable for everything it does against us, against our people, against Europe, and the whole free world."