The Ukrainian Air Force has reported "ballistics on Kyiv," as air defense measures were activated in the capital city.

Kyiv's Mayor Vitaly Klitschko said three people have been injured in the ongoing, overnight attacks. He said in a post on Telegram that Russian drones are "entering the city" and urged people to "stay in shelters."

Of those injured, two were hospitalized and one was treated on the spot, Klitschko said in an update.

The mayor said medics were "heading to the scene" in an earlier post on Telegram after the attacks began.

Metro tracks between two stations in Kyiv were damaged from the attacks, but there was no fire or casualties, the head of the Kyiv City Military Administration Timur Tkachenko said via Telegram.

He wrote in an earlier post that the city is under a "combined attack."

"Our air defense calculations are doing everything possible. But we must protect each other! Stay safe," Tkachenko said.

The Ukrainian Air Force also reported cruise missiles heading towards Lutsk, Chernihiv, Lviv, and the Rivne regions of Ukraine around 4:30 a.m. local Ukrainian time.

Earlier there were preliminary reports that a "high-rise building was hit" in Chernihiv, a city northeast of Kyiv, the head of the Chernihiv City Military Administration Dmitry Bryzhynskyi wrote via Telegram.

"The city is currently under attack," Bryzhynskyi added.

The escalation of attacks between Ukraine and Russia comes as U.S.-brokered peace talks between the countries have failed to come to fruition. High-level delegations from both Ukraine and Russia met in Istanbul, Turkey, on Monday for a second round of talks, but the proposed memorandums presented by each delegation have not moved forward in any meaningful way.

In a phone call between Russian President Vladimir Putin and President Donald Trump on Wednesday, the memorandums for a potential peace deal presented Monday were not discussed, Putin's aide Yuri Ushakov told reporters.

A U.S. official also said this week that there was evidence that Russia was preparing to retaliate against Ukraine for the drone strikes that targeted Russian military sites on Sunday.

At least 11 Russian bomber aircraft and one large transport plane were badly damaged or destroyed in Ukraine's drone attack against Russia, according to satellite imagery reviewed by experts and ABC News.

The covert operation was described as one for the "history books" by Ukraine's President Volodymyr Zelenskyy.

This is a developing story. Please check back for updates.