Russian strike on residential building kills 15 in eastern Ukraine, officials say

 (CNN) -- At least 15 people have been killed after a Russian strike hit an apartment block in the Donetsk region in eastern Ukraine, Ukrainian authorities said Sunday, adding that many others may still be trapped under the rubble.

The residential building in the town of Chasiv Yar was hit on Saturday evening as Russia once again ramped up its assault on cities and towns in eastern Ukraine in an attempt to take control over the entire Donbas area.

The State Emergency Service said that the bodies of 15 people had been found in the rubble so far and that the search and rescue works continued.

As of 1 p.m. local time (6 a.m. ET), emergency workers rescued five people and established contact with three others who were still buried under the rubble, the service said in a statement.

The emergency service added that 24 people, including one child, "may still be under the rubble."

Pavlo Kyrylenko, the head of Donetsk regional military administration, told Ukrainian television that the area was struck by two or three Russian rockets and that the incident was "yet another confirmation of the crimes of the Russian Federation, confirmation that they are shelling residential areas."

Chasiv Yar and other towns in Donetsk have been under heavy fire in recent days as Russian forces try to grind down Ukrainian resistance in the area and move further west towards Kramatorsk and Slovyansk.

The Russian Defense Ministry claimed on Saturday that its troops destroyed a hangar with US supplied M777 howitzers, long-range weapons, and dozens of Ukrainian "militants" near Chasiv Yar.

CNN cannot independently verify the Russian claims. Ukrainian officials said the strike hit a railway station in Chasiv Yar and that several people were injured in the attack.

Donetsk and Luhansk are the two regions that together form the Donbas, the eastern part of Ukraine where the conflict between Ukraine and Russian-backed separatists started in 2014. The area has become the key centerpiece of Russian President Vladimir Putin's military ambition in Ukraine after his troops failed to take over Kyiv earlier this year.

Russian troops have already taken over almost all of the Luhansk region, the head of Luhansk's region military administration Serhiy Hayday said in a telegram post on Saturday, adding that some 300,000 people from the area have been forced to flee their homes.

Lysychansk, the last city that was still under Ukrainian control in Luhansk, fell to Russia last week.

Russian troops have since focused on the Donetsk region, shelling wide areas along the front line and pushing from the Luhansk region into the Donetsk region, according to Hayday.

The Ukrainians have been defending this area against Russian attacks for more than a month.

"We are trying to contain the armed formations of the Russians along the entire front line," Hayday said, adding that "the occupying forces achieved minor successes and continue their offensive to the west of Lysychansk."

Attacking Russian supply lines

Meanwhile, Ukraine continued its campaign to attack Russian supply lines and ammunition storage sites in the occupied areas well behind the front lines.

Ukrainian said a long-range strike hit a Russian military unit in the occupied region of Kherson in southern Ukraine.

Serhii Khlan, a member of Kherson's regional council, said Sunday there had been "a precise hit at the military unit of the occupiers" in Kherson city. Images and video geolocated to Kherson showed a thick column of gray smoke rising into the air Sunday morning.

Khlan told Ukrainian television that Russia aid defenses were not able to intercept Ukrainian artillery fire "thanks to modern Western weapons" the Ukrainian troops are using.

The attack on Sunday followed a series of explosions on Saturday near Kherson. Ukrainian officials said the Ukrainian military struck Russian military stockpiles at the airport in Chornobaivka, just north of the city.

The Mykolaiv and Kherson regions have also become hotspots in the conflict, with Ukrainian forces stepping up their firing against Russian storage and supply lines in occupied territory in the south and Russia using artillery fire to try to prevent Ukrainian advances.

The Russian state news agency RIA Novosti said early Saturday that air defenses had been activated in Kherson.

RIA Novosti cited the pro-Russian military-civil administration as saying that there was shelling from the Mykolaiv direction. "Air defense is working over Kherson," the administration said on its Telegram channel.

The United States has announced its fresh supplies of weapons and humanitarian aid for Ukraine in recent days.

The Biden administration will provide Ukraine with four more high mobility artillery rocket systems in the latest security assistance package, a senior defense official said Saturday. And the US State Department has announced an additional humanitarian aid package for Ukraine totaling nearly $368 million.