At least 15 people were killed and 24 others were feared buried after Russian missiles hit a city in eastern Ukraine, destroying part of a five-story apartment building, officials said Sunday.

Photos and a video of what appeared to be the aftermath of the attack in Chasiv Yar in Donetsk province showed grim-faced rescuers atop a huge pile of rubble. They sifted through broken bricks, mangled metal wiring and crumbled cement beams next to a half-collapsed building.

The images were shared by Pavlo Kyrylenko, the governor of Donetsk Oblast in the eastern Donbas region, and the Internal Affairs Ministry.

“The search and rescue operation continues,” Kyrylenko told Ukrainian television. “We have more proof of Russia’s crimes, that they shell residential areas of any community, whether it’s close to the front lines or not.”

Kyrylenko said that at least 24 people, including a 9-year-old child, might still be under the wreckage and that rescuers managed to establish contact with two of them.

Ukraine’s state emergency service said 15 people were confirmed to have been killed so far.

In the video, heavy machinery can be heard whirring as rescuers inspect tiny crevices in the ruins. Another video shared by Ukraine’s interior ministry shows rescuers carrying white bags containing what appear to be bodies.

“The Russians hit a high-rise apartment building with civilians again,” tweeted Andriy Yermak, the chief of staff to the Ukrainian president.

NBC News could not confirm the Ukrainian officials' version of events.

There was no immediate reaction from the Kremlin. NBC News has asked Russia’s Defense Ministry for comment. 

Ukraine has accused Moscow of launching a barrage of missile strikes on its cities in recent weeks, one of them on a busy shopping center in central Ukraine last month, and targeting civilians.

While Moscow denies targeting civilians in Ukraine, its forces have been behind the heavy bombardment of population centers such as Mariupol, Kharkiv and Sievierodonetsk.

Saturday's missile strikes, part of Moscow's drive to conquer Ukraine's industrial heartland in the historically pro-Russian east of the country, came as its forces appeared to be gearing up for an intensification of its drive west.

The Ukrainian military reported clashes with Russian troops on front lines in the east and the south Sunday. 

Military analysts have said Russia is likely to escalate its offensive in the east after it gained full control of Luhansk province this month, setting the stage for the next phase of the invasion.

Luhansk and Donetsk province form Ukraine’s eastern industrial heartland of the Donbas, which has become the primary focus of the invasion for Russian President Vladimir Putin. 

Before the February invasion, Moscow-backed separatists in the Donetsk and Luhansk regions fought Ukrainian forces for eight years in a grinding conflict that killed thousands of people, which the Kremlin used as a premise to launch the conflict.

After Russia celebrated a major victory in Luhansk last week, there were signs it might be gearing up for a decisive new assault.

The British military said in its daily update Saturday that Russia was moving its reserve forces from across the country and assembling them near Ukraine for future offensive operations.

The Institute for the Study of War, a U.S.-based military think tank, said last week that Russian forces in Ukraine were conducting an “operational pause” while still engaging in limited ground attacks to set conditions for more significant offensive operations in the future. 

Putin warned Thursday that his army “hasn’t really started” to fight in Ukraine yet.