Russia-Ukraine updates: Russian missiles hit close to nuclear reactors: IAEA director

It is vital that Ukraine retakes territory in the south of the country before winter sets in, according to an adviser to President Volodymyr Zelenskyy.

Serhiy Leshchenko told ABC News that any military offensive would be much harder during the winter.

The Ukrainian government fears that Russia could use a deadlock during the winter to consolidate its control over newly occupied territories in the Kherson and Zhaporizhia regions, he said, and it's therefore crucial for Ukraine to counterattack effectively during the coming months.

"Our concern is that if winter comes, under Russian occupation of these territories, Russia will use this three, four months of the winter for fast integration of these territories into Russia," Leshchenko said, "and that is why it is very important to have counterattack in the south before winter starts to take them out from this territory before winter starts."

The presidential adviser also renewed calls for the United States to provide more High Mobility Artillery Rocket Systems or HIMARS.

On Friday, the Biden Administration announced it would provide four more HIMARS to Ukraine on top of the eight that had already been delivered.

Leshchenko said Ukraine was grateful for the 12 HIMARS but that it was nowhere near enough.

"You provided good weapons, but... it's not enough," he said. "Twelve HIMARS is better than nothing, but it’s better that we have not 12, but 112."

"It would change the situation on the front line dramatically and very fast," he added.

-ABC News' Tom Burridge

At least six survivors have been rescued Sunday from the rubble of three apartment buildings purportedly hit by Russian missiles in the Donetsk region of eastern Ukraine, but emergency officials said at least 24 people, including a 9-year-old child, remain unaccounted for and are feared buried under the debris.

At least 15 people were killed when four Russian rockets slammed into the residential buildings Saturday evening in the town of Chasiv Yar, according to Viacheslav Boitsov, deputy chief of emergency service in the Donetsk region.

"They were likely Iskander missiles. A part of a building collapsed, from the fifth to the first floor. There are likely injured people still (under the rubble)," Boitsov told The Associated Press.

Pavlo Kyrylenko, governor of the Donetsk region that includes Chasiv Yar, told The AP that as many as 24 people were believed still trapped in the rubble, including a 9-year-old child.

Russian officials claimed its forces struck Ukrainian army hangars storing U.S.-produced M777 howitzers, a type of artillery, near Kostyantynivka in Donetsk region, but, so far, it has not claimed responsibility for the missile strike on the residential building in Chasiv Yar.

The latest rescue came late Sunday when emergency workers rescued a man after a lengthy operation to free him from under the concrete. Video showed a rescue team carrying the man out of the ruins on a stretcher. He was whisked away to a hospital. It was not immediately clear how severely injured he was.

Emergency Services officials said the latest rescue brought to six the number of survivors dug out of the rubble.

Cranes and excavators worked alongside rescue teams into the night to clear away the ruins of one building, its walls wholly shorn off by the impact of the strike.

At least 15 people were killed and two dozen more are feared trapped in rubble after Russian Uragan rockets slammed into a five-story apartment building in eastern Ukraine's Donetsk region, local officials said on Sunday.

Search-and-rescue workers were combing through the rubble for survivors on Sunday.

The missile strike came as Ukrainian officials reported clashes with Russian troops on the frontline in the eastern and southern Ukraine.

Donetsk Governor Pavlo Kyrylenko said the strike on the apartment building occurred Saturday evening in the town of Chasiv Yar. The regional emergency service said Sunday that the death toll had climbed to 15 and that 24 more people could still be buried under the rubble.

"We ran to the basement, there were three hits, the first somewhere in the kitchen," a local resident, who gave her name as Ludmila, told rescuers as they removed a body wrapped in a white sheet and cleared rubble using a crane as well as their hands. "The second (strike), I do not even remember, there was lightning, we ran towards the second entrance and then straight into the basement. We sat there all night until this morning."

Andriy Yermak, chief of staff to Ukrainian President Volodymyr Zelenskyy, said in a Telegram post that the strike was "another terrorist attack" and that Russia should be designated as a state sponsor of terrorism as a result.

Russian officials claimed its forces struck Ukrainian army hangars storing U.S.-produced M777 howitzers, a type of artillery, near Kostyantynivka in Donetsk region, but, so far, has not claimed responsibility for the missile strike on the residential building in Chasiv Yar.

-ABC News' Christine Theodorou

U.S. Secretary of State Antony Blinken said Sunday that the Russian invasion of Ukraine has "significantly exacerbated" a global food insecurity crisis and may have contributed to the economic collapse of Sri Lanka.

“What we are seeing around the world is growing food insecurity that has been significantly exacerbated by the Russian aggression against Ukraine and as we've had opportunity to discuss in recent days, there are more than 20 million tons of grain that are sitting in silos in Ukraine that can't get out can't get out to feed people around the world," Blinken told reporters during his first official visit to Thailand.

He noted that he discussed the global food insecurity crisis during meetings with Thai Deputy Prime Minister and Foreign Minister Don Pramudwinai and said a memorandum of understanding the two leaders signed commemorating a new collaboration will "make it easier for Thailand and the United States to quickly share information and consult on possible supply chain disruptions so that we can actually take early action to mitigate problems."

Blinken added that the impact of this Russian invasion of Ukraine is being felt around the world, particularly in Sri Lanka, where the prime minister said late last month that the island nation’s debt-laden economy had “collapsed” and run out of money to pay for food and fuel. The economic turmoil has prompted massive protests in Sri Lanka and over the weekend demonstrators stormed the president's residence in the capital of Colombo.

"So we're seeing the impact of this Russian aggression to play out everywhere," Blinken said. "Again, it may have contributed to the situation in Sri Lanka. We’re concerned about the implications that it has around the world."

-ABC News' Lauren Minore