At least 30 people were killed in a strike on a Ukrainian military barrack south of Mykolaiv on Friday, according to a witness.

A civilian working with the Ukrainian military told ABC News that more than 30 people were killed in the attack– believed to be in retaliation to damage done to the Russian controlled facility in Kherson.

On Friday, Mykolaiv's mayor said that "dozens" of troops were killed in the strike.

Mykolaiv's governor said the rescue operation is ongoing and no official figures on casualties will be released until it's over.

-ABC News' Dada Jovanovic

The United Nations Children's fund warned Saturday that children fleeing the war in Ukraine are at an increased risk of human trafficking and exploitation.

"Traffickers often seek to exploit the chaos of large scale population movements, and with more than 1.5 million children having fled Ukraine as refugees since [Feb.24], and countless others displaced by violence inside the country, the threat facing children is real and growing," UNICEF said.

According to an analysis conducted by UNICEF and the Inter-Agency Coordination Group against Trafficking, 28% of identified victims of trafficking globally are children.

"In the context of Ukraine, UNICEF child protection experts believe that children would likely account for an even higher proportion of potential trafficking victims given that children and women represent nearly all of the refugees who have fled the country so far," UNICEF said.

According to UNICEF, more than 500 unaccompanied children were identified crossing the Ukrainian border into Romania between Feb. 24 and March 17. It also estimates that the true number of separated children who have fled Ukraine is likely much higher.

"Displaced children are extremely vulnerable to being separated from their families, exploited, and trafficked. They need governments in the region to step up and put measures in place to keep them safe," said Afshan Khan, UNICEF’s regional director for Europe and Central Asia.

Khan said children need to be screened for their vulnerability as they cross the border into another country.

"UNICEF is calling on governments to improve cross-border collaboration and knowledge exchange between and among border control, law enforcement and child protection authorities and to quickly identify separated children, implement family tracing and reunification procedures for children deprived of parental care," UNICEF said.

UNICEF also said additional screening for protection risks should be implemented in shelters, large urban train stations and other locations where refugees gather or pass through.

The West has proven to be unreliable as an economic partner and a place for keeping foreign exchange reserves, Russian Foreign Minister Sergei Lavrov said Saturday.

"Even disregarding the situation with Ukraine and the sanctions, conduct of the West proves that it is unreliable both as a part of the world where major reserve currencies are generated, as an economic partner, and as a country where forex reserves could be kept. They might easily be stolen," Lavrov told finalists of the international stage of the Leaders of Russia competition.

This is why Russia is strengthening cooperation with other countries, including China, he said.

Lavrov also commented on the reinstatement of the Joint Comprehensive Plan of Action, which would allow Iranian oil supply on the global market.

"We never betray our friends in politics. Venezuela is our friend, and Iran is a state that is very close to us. Secondly, we do not pursue selfish interests, unlike the Americans," Lavrov said in response to a question whether the JCPOA reinstatement was advantageous to Russia.

"You can see what they [the Americans] are actually doing, trying to spite Russia and teach it a lesson," he said.

"So, the Americans have been contacting Saudi Arabia, the Emirates and Qatar regarding oil and gas. All of those countries, just like Venezuela and Iran, clearly said: when we discuss issues pertaining to the appearance of new actors in the oil market, all of us are committed to the OPEC+ format, where quotas for every actor are discussed and agreed upon by consensus," he said.

"For now, I see no reason to believe that this mechanism may somehow be dismantled. No one is interested in that," Lavrov said.

At least 112 children have been killed since the Russian invasion of Ukraine began, the local Juvenile Prosecutor’s Office said.

More than 140 children have been wounded during the first 24 days of the war, officials said.

Fifty-seven children have been killed in Kyiv, officials said. Another 36 were killed in Kharkiv and 28 were killed in the Donetsk Oblast, they said.

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