Ukrainian President Volodymyr Zelenskyy on Sunday wished Ukrainian military forces success in what he described as the "main battles" that are "coming soon."

Zelenskyy's statement came a day after he said at a news conference in Kyiv that Ukrainian forces will soon launch a counteroffensive, likely before F-16 fighter jets promised by Western allies arrive.

"Dear warriors, the main battles are coming soon. We must free our land and our people from Russian slavery,” Zelenskyy said at an event where he bestowed medals to members of the county’s Border Guard forces.

Ukrainian President Volodymyr Zelenskyy said the Ukrainian counteroffensive will start before Ukraine receives F-16 fighter jets sought from Western countries.

"Frankly speaking, it would help us a lot. But we also understand that we can't drag it [the counteroffensive] out, which is why we'll start before we receive F-16 [aircrafts] or other models," Zelenskyy said at a news conference for Scandinavian media held in Kyiv on Saturday, according to a script provided by Reuters.

He added, "But to calm Russia down with the fact that we'd still need a couple of months to train on the aircrafts and only then we'd start; No, this won't happen. We'll start and go forward, while at the same time, simultaneously, I think this is very important [to receive western fighter aircrafts.]"

He said Ukraine is "capable of putting an end to this war."

Also on Saturday, Ukraine's Foreign Minister Dmytro Kuleba said Ukraine received a signal from some countries about the readiness to start training Ukrainian pilots on F-16 fighter jets.

According to Kuleba, the F-16 fighter jet is the ideal aircraft due to its technical characteristics, although Kyiv does not overlook other aircraft, either. The minister added that the decisive word on issuing F-16s will be with the United States, because these are American fighters.

-ABC News' Edward Szekeres and Max Uzol

A Russian attack on a high-rise building in Uman has left 23 people dead. Among the dead were six children between the ages of one and 17 years old, according to the Ukrainian Minister of Internal Affairs, Ihor Volodymyrovych Klymenko.

Rescuers, policemen and volunteers managed to save 17 people from the rubble. Heavy machinery and special equipment were involved, according to officials.

Two more women are considered missing, officials said. But the search and rescue operation has concluded, officials said.

"My sincere condolences to the relatives of the deceased. We will punish this evil. We will not allow it to grow. We will definitely stand up and win," Klymenko said.

-ABC News' Tatyana Rymarenko

Russian airstrikes targeted several cities across Ukraine early Friday, killing at least 25 people, Ukrainian officials said.

The city of Uman in central Ukraine's Cherkasy Oblast was the worst affected. Several buildings were damaged or destroyed. One of the strikes hit an apartment building, killing at least 23 people, including four children, and injuring another 18 people, according to Cherkasy Oblast Gov. Ihor Taburets. The attack happened at around 4:30 a.m. local time, when most people would have been asleep. An entire section of the nine-story building collapsed, with 27 apartments completely destroyed. There were 109 people who lived in that part of the building, according to Ukrainian police. Rescue teams were expected to spend all day and night searching for survivors in the rubble.

It was the deadliest single attack on civilians in Ukraine since January.

Dnipro, Ukraine's fourth-largest city and a major industrial hub located in southeastern Dnipropetrovsk Oblast, was hit by "high-precision" strikes in the early morning hours, leaving a woman and a 3-year-old child dead, according to Dnipro Mayor Boris Filatov.

Russian strikes also targeted Kyiv, Ukraine's capital and largest city, but there were no reports of any casualties or damages. It was the first such attack on the capital in 51 days, according to the Kyiv City Military Administration. Preliminary data shows 11 cruise missiles and two drones were destroyed in Kyiv's airspace, the city military administration said.

-ABC News' Yulia Drozd, Will Gretsky, Natalia Kushnir and Joe Simonetti

One year ago, with Ukraine's borders surrounded by what seemed to be a superior military force, many U.S. officials and analysts predicted a swift Russian blitz to Kyiv.

But after Russian President Vladimir Putin sent his more than 150,000 arrayed troops across the border, it soon became clear that a dual reassessment was in order: The Russian invaders were less potent than advertised, and the Ukrainians were unexpectedly stubborn and wily in the defense.

Some of the Russian troops weren’t even aware they were on a combat mission until Ukrainian bullets came cracking past them, according to U.S. officials. Meanwhile, Ukrainian forces stalled a massive Russian supply convoy through direct attacks and by destroying a key bridge. Only one week into the invasion, Putin's men were plagued with food and fuel shortages, morale running similarly low.

Kyiv stood.

"Putin assumed that Ukraine was an easy target, Putin assumed that Kyiv would easily fall, and Putin assumed that the world would stand by," U.S. Secretary of Defense Lloyd Austin said during a speech in Brussels last week. "But the Kremlin was wrong on every count."

Ukrainian forces were armed with more than grit.

They also had years of U.S. and NATO military training, plus American-made weapons, like anti-armor Javelins and anti-aircraft Stinger missiles. These made Russian vehicles vulnerable to ambush, and left Russian helicopter and jet pilots wary of flying over Ukrainian positions. Indeed, many airmen did not return from their sorties.

Despite astonishing losses of soldiers and vehicles, Putin has shown no inclination to end the conflict anytime soon. And despite its tenacity, Ukraine has also taken significant casualties, and is not able to produce enough of its own weapons and ammunition to keep up the fight.

Ukraine, after thwarting the advance on its capital, and later routing Russian forces from Kharkiv, now largely faces a battle of supply.

"When this war began, Russia had a larger population, a much bigger defense budget, a bigger military, bigger industrial base. So, this became an industrial war and a war of industrial bases," said Seth Jones, director of the International Security Program at the Center for Strategic and International Studies. "This is why Western industrial support has been so critical."

A key question now is, despite massive military aid packages and a promise to send even more, could the U.S. strategy ultimately result, not in a Ukrainian victory, but a stalemate in a years-long war of attrition?

-ABC News' Matt Seyler