Russian President Vladimir Putin has escalated his strikes on Ukrainian cities in the wake of a series of battlefield setbacks that have weakened his military’s grip on territory it claims to have annexed as well as the Kremlin’s hold over the mood at home.

Kyiv Mayor Vitali Klitschko said "kamikaze" drones caused five explosions that rocked the city in the early morning hours on Monday. One of them hit a residential building in the central Shevchenkivskyi District, the mayor said.

Kyrylo Tymoshenko, the deputy head of the Ukrainian president’s office, said 19 people were rescued from the building, but three have been confirmed dead. The rescue operation was ongoing, he said.

Klitschko later said a pregnant woman and her husband were among the dead.

NBC News has not verified the reports.

Rescuers were working fast to clear out the rubble, looking for anyone missing after several floors appeared to have collapsed. The air was filled with a smell of fire and smoke, as well as dust from the rubble.

Speaking with NBC News at an intersection close to the damaged building, Kyiv resident Anna Frolova said the morning was off “to a horrible start” as she thought the Russians “had enough” with last week’s strikes on key infrastructure in her city. “It turns out they have not had enough, and now they are hitting residential buildings as well and people are dying. And this is scary,” said Frolova, 52.

“I feel fear, pain, anger and hate,” she added, vowing to stay in the capital despite the strikes. “Hate toward, I don’t know, these people who have allowed this to happen in the 21st century. This Medieval war.”

After the first round of air-raid sirens ended around 9:30 a.m. local time (2:30 a.m. E.T.), life seemed to have quickly returned to relative normality on what turned out to be a sunny, mild day. The city’s center was full of cars and people as the threat of another nosediving drone dissipated, only for the warnings to soon return.

Ukrainian officials also reported rocket strikes in the southern port city of Odesa, central Dnipropetrovsk region and the northeastern Sumy region. Overnight, drone attacks were also reported by officials in the southern city of Mykolaiv, where deadly rocket strikes last week destroyed the two top floors of a residential building.

"All night and all morning, the enemy terrorizes the civilian population," President Volodymyr Zelenskyy said in a statement shared on the Telegram messaging app Monday. "Kamikaze drones and missiles attack all of Ukraine."

The head of Zelenskyy's office, Andrii Yermak, called for more air defense systems from the West and "as soon as possible."

Klitschko shared an image of what he said was wreckage of one of the drones involved in the attack on Kyiv, displaying a Russian name for Iranian-made Shahed-136 drones that both Washington and Kyiv have accused Tehran of supplying to Moscow to be used in Ukraine. Iran has denied the claims. NBC News could not verify the photo.

The mayor said that, in all, 28 drones flew in the direction of Kyiv Monday morning, but the majority of them were shot down.

While not directly acknowledging drone strikes on Kyiv, Russia's defense ministry said Monday it used "high-precision long-range air and sea-based weapons" to strike what it said were military and energy targets in Ukraine.

Zelenskyy warned earlier this month about Russia’s increasing use of Iranian-made drones, posing a new challenge for the country’s air defenses and causing concern among Ukraine's Western allies over Tehran's alleged support for Russia in the war.

The Shahed-136 drones, which have earned the nickname “kamikaze” for destroying its target by physically crashing into it, are relatively cheap and can be equipped with a small warhead, making it an effective precision weapon, military analysts told NBC News.

Its operational range is subject to debate among analysts, but could be as long as 1,200 miles, although it’s probably much shorter in practice, but still sufficient to hit any target in Ukraine from Russian-occupied areas.

Yuriy Ihnat, spokesman for the Air Force Command of the Ukrainian Armed Forces, said during a briefing Monday that the country's air defense systems destroyed 85% of the Iranian drones that Russia had used to attack Ukraine since Sunday evening. NBC News could not verify the claim.

Last week's attacks were framed by Putin as revenge for a blast that damaged his signature bridge from Russia to the annexed Crimean Peninsula.

The aerial aggression inspired renewed support from Kyiv's Western allies, with President Joe Biden vowing to provide the advanced air defense systems Ukraine desperately wants in order to fend off such attacks.

The White House was previously reluctant to put the technology in play in Ukraine, fearing it would be seen by Russia as a step closer to direct involvement in the war.