The United Nations said it's verified the deaths of nearly 100 children in Ukraine in April alone -- and officials believe the actual figure to be considerably higher.

"More children have been injured and faced grave violations of their rights, millions more have been displaced," UNICEF Deputy Executive Director Omar Abdi said at Thursday's U.N. Security Council meeting. "The war in Ukraine, like all wars, is a child protection and child rights crisis."

Education also "came to a standstill" when Russia invaded, Abdi said.

One in every six UNICEF-supported schools in eastern Ukraine was damaged or destroyed as of last week, Abdi said.

"These attacks must stop. All parties must honour their legal and moral obligation to protect civilians and civilian infrastructure, to respect international humanitarian and human rights law, and to ensure the rights of children are upheld," Abdi said.

-ABC News' Christine Theodorou

"Difficult" negotiations are underway between Ukraine and Russia to coordinate the evacuation of seriously wounded fighters from the Azovstal steel plant in Mariupol in exchange for an unspecified number of Russian prisoners of war, Ukrainian Deputy Prime Minister Iryna Vereshchuk said.

"We are currently negotiating only 38 severely wounded fighters that can't walk," she said.

-ABC News' Irene Hnatiuk

Russia "will be forced to take retaliatory steps both of military-technical and of other nature in order to stop the threats to its national security" in response to Finland’s possible accession to NATO, according to state-run TASS citing a statement by the Russian Foreign Ministry.

The ministry added, "Finland joining NATO will seriously harm bilateral Russian-Finnish relations and the maintenance of stability and security in the North European region."

Russia will conduct a "special analysis" and take necessary measures for national security if Finland joins NATO, Kremlin spokesman Dmitry Peskov said Thursday.

"There is an order from the president, the supreme commander-in-chief, that a list of measures be composed to strengthen our western flanks in connection with the strengthening of the eastern flank of NATO," Peskov told reporters during a daily briefing. "NATO has been enlarging towards us. So, clearly, all of that will be elements of a special analysis and the elaboration of measures necessary for maintaining a balance and providing our security."

"Everything will depend on the manifestation of the further [NATO] enlargement process -- how far the military infrastructure will grow towards our borders," he added.

When asked whether Finland's accession to NATO -- the world's biggest military alliance -- would pose a threat to Russia, Peskov told reporters: "Of course it will."

"Another enlargement of NATO does not make our continent more stable and secure," he said.

Peskov's comments followed a joint statement released by Finnish President Sauli Niinisto and Finnish Prime Minister Sanna Marin announcing their support for Finland applying to join NATO.

White House national security advisor Jake Sullivan hinted Thursday of more sanctions coming against Russia in the "next week or two" aimed at targeting ways Moscow is evading sanctions already imposed.

“Where our focus will be over the course of the coming days is on evasion,” Sullivan said Thursday at the Economic Club of Washington. “As Russia tries to adjust to the fact that it’s under this massive economic pressure, what steps do they take to try to evade our sanctions and how do we crack down on that? And I think we'll have some announcements in the next week or two that identify targets that are trying to facilitate that evasion both inside Russia and beyond."

When Sullivan was asked whether sanctions will automatically be lifted if a negotiated peace deal between Russia and Ukraine is worked out, he appeared cautious with his words, saying, “a lot of that depends on what the shape and scope” of the agreement is.

“A lot of it depends on what the Ukrainians, in consultation with us and the Europeans come to agree to," Sullivan said. "You know, we're not going to do a deal over the head of the Ukrainians where we give a bunch of sanctions relief to Russia. But if some measure of sanctions relief were built in to some credible diplomatic solution led by the Ukrainians, that's something that we would happily discuss."

But Sullivan said Russian oligarchs shouldn't expect to ever get back their yachts and other assets seized under sanctions that have been imposed, saying the ultimate goal is "not to give them back” once the war is over.

“The president is actively looking at how we can deal with the fact that as we seize these assets, our goal is not to give them back. Our goal is to put them to a better use than that," Sullivan said. "But I'll be careful in what I say today because there's an ongoing kind of policy process around how we end up dealing with that question. But, rest assured, that the goal is not just to sit on them for a while."

-ABC News' Justin Gomez