Video has emerged showing Ukrainian rescuers working to remove unexploded devices from civilian homes amid the Russian invasion.

The video, released Friday by the State Emergency Service of Ukraine and verified by ABC News, shows pyrotechnic units in the northern city of Chernihiv using special equipment to carefully search for and remove shells, missiles and mines that landed in houses but didn't explode.

The State Emergency Service of Ukraine said it was called in to seize ammunition 18 times over the past day. The agency warned people not to approach the objects because they could explode "at any time" and to immediately report such findings to rescuers or police.

-ABC News' Victoria Beaule

U.S. President Joe Biden departed Belgium on Friday morning and was en route to Poland for the final leg of his four-day trip aimed at maintaining unity among allies and supporting Ukraine's defense against Russia.

Biden was seen boarding Air Force One in the European Union's de facto capital, Brussels, at 6:42 a.m. ET. He is expected to land in Rzeszow, Poland, at around 9:15 a.m. ET, where he will receive a briefing on the humanitarian response to the millions of people fleeing Ukraine in the wake of Russia's invasion. He will also meet with service members from the U.S. Army's 82nd Airborne Division.

-ABC News' Molly Nagle

About 300 people were killed last week in a Russian airstrike on a drama theater-turned-bomb shelter in the besieged Ukrainian city of Mariupol, the city's government said Friday, citing eyewitnesses.

"We didn't want to believe in this horror," the Mariupol City Council. said in a statement. "But the words of those who were inside the building at the moment of this terrorist act say the opposite."

As many as 1,500 civilians had been taking refuge in the grand, columned Donetsk Regional Theatre of Drama in central Mariupol when it was struck on March 16, according to the Ukrainian government. Satellite images showed huge white letters on the pavement in front of and behind the building spelling out "CHILDREN" in Russian -- "DETI" -- to alert warplanes to those inside.

Video circulating online and verified by ABC News shows the immediate aftermath of the strike on the theater. People covered in dust are seen trying to make their way out of the theater, walking down from the first floor staircase in an area of the building that was still standing at the time.

Since invading Ukraine on Feb. 24, Russian forces have been relentlessly bombarding Mariupol, destroying homes and leaving thousands of residents trapped. Ukraine has defied Russia's ultimatum for its troops to lay down arms and surrender the strategic southeastern port city of 430,000.

-ABC News Patrick Reevell

Russia claimed Friday that its forces had captured five more localities in Ukraine.

"The grouping of troops of the Russian Armed Forces advanced another 4 kilometers overnight and captured Batmanka, Mikhailovka, Krasny Partizan, Stavki and Troitskoe," the Russian Ministry of Defense said in a statement.

Ukraine did not immediately comment on the claim.

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