Ivan Fedorov, the mayor of the occupied Ukrainian city of Melitopol, has been freed after being kidnapped by Russian troops, according to Ukrainian officials.

Fedorov was freed in a "special operation," Kirill Timoshenko, the deputy head of Ukraine's presidential office, said. He didn't give additional information.

His kidnapping was reported on March 11.

Ukrainian President Volodymyr Zelenskyy released a video of him talking to Fedorov on the phone. The president told the mayor he was very glad to speak with him and said, "We don't leave ours behind."

-ABC News' Patrick Reevell

More than half of the 3 million people who have fled Ukraine are children, according to UNICEF.

“We realized that it’s about 75,000 a day… that’s about 55 Ukrainian children becoming refugees every minute. Essentially, one every second since this war started,” UNICEF spokesperson James Elder told ABC News Live.

Many children are suffering from a lack of food and freezing temperatures, he said.

"Many of them haven’t had clean water in two days,” he said.

Elder also highlighted the psychological trauma.

“They’ve been under bombardment. Many of them have seen family members or community members killed," he said.

Elder added that UNICEF is “desperately concerned” about human trafficking, warning that any large number of children coming into a new country are at a higher risk of being abducted.

-ABC News' Shannon Caturano

President Joe Biden announced more aid to Ukraine Wednesday, saying that the "American people are answering [Ukrainian] President [Volodymyr] Zelenskyy's call for more help, more weapons for Ukraine to defend itself, more tools to fight Russian aggression."

Biden announced an additional $800 million in military assistance as part of the $13.6 billion aid package for Ukraine contained in the government spending bill Biden signed into law Tuesday, which includes weapons the Ukrainians have been requesting, such as anti-armor and anti-air systems.

“At the request of President Zelenskyy, we have identified and are helping Ukraine acquire additional longer range anti-aircraft systems and ammunitions for those systems," Biden said. "Our new assistance package also includes 9,000 anti-armor systems -- these are portable, high-accuracy systems, shoulder-mounted missiles, that the Ukrainian forces have been using."

The U.S. is also sending drones, "which demonstrates our commitment to sending our most cutting-edge systems to Ukraine for its defense," Biden said.

The new package will also supply Ukraine with machine guns, shotguns and grenade launchers.

"This could be a long and difficult battle," Biden said. "But the American people will be steadfast in our support of the people of Ukraine in the face of [Russian President [Vladimir] Putin’s immoral, unethical attacks on civilian populations. We are united in our abhorrence of Putin’s depraved onslaught, and we are going to continue to have their backs as they fight for freedom, their democracy, their very survival."

Biden did not directly address Zelenskyy's emotional appeal to lawmakers on Wednesday for the U.S. to back a no-fly zone, which the administration has repeatedly rejected.

-ABC News' Libby Cathey and Molly Nagle

By a vote of 13-2, the United Nations' highest court, the International Court of Justice, made a preliminary ruling that Russia "shall immediately suspend military operations."

The two votes against were from Russia and China.

Ukrainian President Volodymyr Zelenskyy reacted on Twitter, writing that “Russia must comply immediately." But the ruling is mostly symbolic as the ICJ has no direct means to enforce it.

-ABC News' Cindy Smith

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