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

Russia's security services have arrested an anti-Kremlin political commentator who the jailed Wall Street Journal reporter Evan Gershkovich met with shortly before his own arrest.

Yaroslav Shirshikov has said he spent two days showing Gershkovich around the city of Yekaterinburg during a reporting trip there a couple of weeks before Russia seized Gershovich.

Shirshikov said he had been due to meet with Gershkovich again the week the reporter was arrested in the city.

This morning, local media published video showing masked security officers detaining Shirshikov in his apartment and searching it.

A local news outlet cited a security services representative saying Shirshikov may have been arrested for posting comments cheering the assassinations of two ultra-nationalist pro-war figures, Daria Dugina and the blogger Vladen Tatarsky.

The site UralLive quoted a law enforcement source that Shirshikov was detained on a charge of “justifying terrorism”, which carries a maximum sentence of 7 years prison. It linked the charge to a social media post in which Shirshikov wrote he wasn’t sad over the death of Tatarsky, who was killed in a bomb attack in St. Petersburg this month.

Shirshikov spoke to several international media outlets including ABC following Gershkovich's arrest. He said that Gershkovich had acted entirely as a professional journalist in Yekaterinburg, conducting interviews openly and doing usual reporting.

Shirshikov is a critic of the Russian government and has spoken publicly about his opposition to the war in Ukraine.

-ABC News' Patrick Reevell