In his latest national address, Ukrainian President Volodymyr Zelenskyy said negotiations with Russia are "ongoing."

"My priorities in the negotiations are absolutely clear: the end of the war, security guarantees, sovereignty, restoration of territorial integrity, real guarantees for our country, real protection for our country," he said in a speech that aired tonight.

Zelenskyy said he addressed both the U.S. and all the relevant states in regard to creating a new union he called U-24. He said that the new alliance will ensure that aggressors receive a coordinated response from the world.

"We can no longer trust the existing institutions. We cannot expect bureaucrats in international organizations to change so quickly," he said. "Therefore, we must look for new guarantees. Create new tools. Take those who have courage and do what justice requires."

The United Nations Security Council will hold an emergency meeting on Thursday to address the humanitarian situation in Ukraine.

The U.S., Albania, U.K., France, Ireland and Norway requested the meeting, according to the Norway U.N. The countries have asked for briefings by the U.N.'s Department of Political and Peacebuilding Affairs, the U.N.'s refugee agency and the World Health Organization.

More thank 3 million refugees have alreay fled Ukraine since the invasion began on Feb. 24, according to the U.N.'s refugee agency.

-ABC News' Will Gretsky

Ukraine’s military said it is trying to launch counter-attacks in northern areas on the edge of Kyiv, seeking to push Russian forces back from the towns at the gates of the capital where they've been bogged down for two weeks.

The sounds of intense shelling and fighting could be heard from the north of Kyiv the last three days. Battles have been raging in the towns of Irpin, Bucha and Hostomel, just a few miles from the city limits and from where thousands of civilians have been fleeing.

"The situation remains difficult, especially in the south and east [of Ukraine]. But more and more often our defenders are moving into counterattacks in various parts of the front: from Kyiv and Mykolaiv regions to the Luhansk region,” Ukrainian officials said in a statement Wednesday, referring to regions in southern and eastern Ukraine.

Authorities have imposed a full curfew from Tuesday evening to Thursday morning, locking down the capital and forbidding people from going outside. Plumes of smoke could be seen rising from the direction of the northern areas and the popping sound of small arms fire heard occasionally throughout the day Wednesday.

-ABC News' Patrick Reevell

"I think he is a war criminal," President Joe Biden said Wednesday of Russian President Vladimir Putin.

The president initially told the reporter "no" when asked if he was ready to label Putin a war criminal, but moments later Biden circled back, asking her to repeat the question.

This marked the first time Biden has called Putin a war criminal since the invasion began. The White House had previously said there was an official review underway before the administration could formally accuse Putin of war crimes.

-ABC News' Mary Bruce

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