President Joe Biden met with Ukrainian refugees in Warsaw, Poland, on Saturday. When asked by reporters what he thought of Russia's President Vladimir Putin after meeting with refugees, Biden said, "He’s a butcher."

Biden was greeted by Warsaw Mayor Rafal Trzaskowski and Polish Prime Minister Mateusz Morawiecki outside the PGE Narodowy Stadium and he met several volunteers and refugees.

After meeting with refugees, Biden briefly spoke with reporters and said he’s always in awe of the depth and strength of the human spirit of refugees.

"I’ve been to an awful lot of places like this, a lot of refugee camps, in my life, and what I’m always surprised by, is the depth and strength of the human spirit. I mean it sincerely. They’re -- it’s incredible. It’s incredible. See all those little children? Just want to hug, they just want to say thanks. I mean -- I mean, it just makes you so damn proud," Biden said.

"Each one of those children said something to the effect, say a prayer for my dad, or my grandfather or my brother, who’s back there fighting. And I remember what it’s like when you have someone in a war zone. Every morning you get up and you wonder. You just wonder, you pray you don’t get that phone call," Biden said.

-ABC News' Armando Garcia

Ukrainian President Volodymyr Zelenskyy made a surprise video appearance at the Doha Forum in Qatar, addressing the energy-rich nation directly, calling on it and other energy-producing countries to increase energy production.

"The responsible states, in particular the State of Qatar, are reliable and reputable suppliers of energy resources. And they can contribute to stabilizing the situation in Europe. They can do much to restore justice," Zelenskyy said.

Zelenskyy added, "The future of Europe depends on your efforts! I urge you to increase energy production! So that Russia understands that no state should use energy as a weapon to blackmail the world."

Zelenskyy also warned that a food crisis will come after the migration crisis.

"Wheat, oil, corn and other agricultural products from our country are the basis of stability and internal security of many countries in different parts of the world… Russian troops mine fields in Ukraine, blow up agricultural machinery, destroy fuel reserves needed for sowing. They blocked our seaports," Zelenskyy said.

Zelenskyy added: "Our state will have enough food. But the lack of exports from Ukraine will hit many nations in the Islamic world, Latin America and other parts of the world. Where some invaders still dream of going to strengthen their old privileges."

Zelenskyy also drew direct comparisons between the destruction of Mariupol and the Russian bombing of Aleppo.

He criticized Russia for threatening the world with nuclear weapons, and called on countries to boost their production to counteract the global dependence on Russian oil.

-ABC News' Guy Davies

President Joe Biden and Polish President Andrjez Duda delivered brief remarks ahead of their expanded bilateral meeting, with both sides stressing their strong relationship, and the importance of unity in the midst of Russian aggression against Ukraine. Biden is set to give a speech in Warsaw later Saturday.

Biden recalled a previous trip he made to Warsaw 25 years ago, after advocating for Poland to Join Nato, and said his message then is the same as today: "For your freedom and for ours."

Biden also reiterated the U.S.'s commitment to NATO's Article 5.

"The single most important criterion in this time-changing world -- so much has changed, not just here, but in other parts of the world -- is that NATO's stay absolutely, completely, thoroughly united. [There needs] to be no separation, and our points of view, and whatever we do, we do in unison, and everyone, everyone comes along," Biden said.

Biden added: "I'm confident that Vladimir Putin was counting on being able to divide NATO, and being able to separate the Eastern flank from the West. To be able to separate nations based on past histories. But he hasn't been able to do it. We've all stayed together. And so I just think it's so important that we, Poland and the United States, keep in lockstep the power pursuit."

Biden also spoke about Poland's work on the humanitarian side of the crisis, praising the country for taking in so many refugees, but acknowledging that it should not be just on Poland to handle the brunt of the load.

"We do acknowledge that Poland is taking on a significant responsibility that I don't think should just be Poland, It should be the whole world -- all of NATO's responsibility. The fact that you have so many, so many Ukrainians seeking refuge and this country of Poland," Biden said.

He added: "We understand that because we have on our southern border thousands of people a day --literally, not figuratively --trying to get into the United States. But we believe that we the United States, should do our part relative to Ukraine as well by opening our borders to another 100,000 people. And with that, and in addition to that, I think it's important that we are in constant contact, about how we each wish to proceed, relative to what Russia is doing, and how to proceed."

-ABC News' Molly Nagle

President Joe Biden arrived at the Polish presidential palace Saturday for a bilateral meeting with Polish President Andrjez Duda, as the Russian invasion of Ukraine continues.

Biden and Duda shook hands and stood shoulder to shoulder as both countries' national anthems played.

Biden was met by three branches of the Polish military, as the two leaders reviewed the troops. They then headed inside for the meeting.

Biden was joined by a delegation of seven U.S. officials, including Secretary of State Antony Blinken and Secretary of Defense Lloyd Austin, who participated in the meeting, according to the White House.

The Polish delegation consisted of six officials, including the ministers of foreign affairs and national defense, according to the White House.

-ABC News' Molly Nagle

All Russian troops have left the Ukrainian cities of Kyiv and Chernihiv, withdrawing north toward the borders of Belarus and Russia to consolidate before likely redeploying to the Donbas region in eastern Ukraine, a senior U.S. defense official told reporters Wednesday.

But even with the Russians gone, the territory remains treacherous.

"There are some indications that they left behind mines and things like that, so the Ukrainians are being somewhat careful in some areas north of Kyiv as they begin to clear the ground and clear the territory and re-occupy it," the official said.

While the U.S. hasn't yet seen these troops redeploy elsewhere in Ukraine, it'll likely happen soon, according to the official. Ukrainian forces are preparing for a major fight in Donbas, the official said.

The official also said the Pentagon is "monitoring" an apparent nitric acid explosion in Ukraine's Luhansk region, which Russia blamed on Ukraine.

"We've seen the Russians claim that this was a Ukrainian attack on this. We do not believe that is true," the official said. "We do believe that the Russians are responsible, but exactly what they used when they did it, why they did it, what the damage is, we just don't have that level of detail," the official said.

The official also noted that a small number of Ukrainians currently in the U.S. for "professional military education" were pulled aside for a couple days of training on Switchblade drones, which the U.S. is sending overseas as part of its military aid, according to the official.

"Although it's not a very difficult system to operate, we took advantage of having them in the country to give them some rudimentary training on that," the official said.

-ABC News' Matt Seyler