Videos on social media showed damage to a children and women's clinic, and the World Health Organization has verified 18 attacks on health care facilities in the country so far

Russian military forces severely damaged a children's hospital and maternity ward in the Ukrainian city of Mariupol, Ukraine President Volodymyr Zelenskyy said Wednesday.

"People, children are under the wreckage," Zelenskyy tweeted. "Atrocity!"

Ukrainian officials said that they are working to determine how many people have been killed or injured from the strike, the Associated Press reported. Mariupol's city council said in a post on the social media site Telegram that the damage is "colossal," and that "until recently, children were treated" at the hospital.

Zelenskyy's tweet included a video of destroyed walls, blasted-out windows and extensive debris. People were shown leaving the facility with injuries in other social media videos, the Washington Post reported.

The World Health Organization said that they've verified 18 attacks on health care facilities in Ukraine so far, including 10 deaths and 16 injuries. By striking health care facilities, "these attacks deprive whole communities of health care," WHO director General Tedros Adhanom Ghebreyesus said.

"Attacks on health care violate international law and endanger lives," WHO said in a tweet. "Health workers, hospitals and ambulances should NEVER be targets."

Along with the deaths and injuries from bombing and gunfire, Russia's invasion has disrupted health care services and created critical drug shortages in Ukraine.

And as thousands of civilians in Mariupol and other cities evacuate to neighboring countries like Poland, Slovakia, Moldova and Romania, the influx could overwhelm their health systems. WHO, which has also delivered extensive supplies to Ukraine, said last week that the countries are managing so far, "but this is as of today," WHO Europe director Hans Kluge told Reuters.

"We have seen in the past that health systems have a breaking point, and the situation is very unpredictable."

Russian forces launched a large-scale invasion on Feb. 24 — the first major land conflict in Europe in decades. Details of the fighting change by the day, but hundreds of civilians have already been reported dead or wounded, including children. More than a million Ukrainians have also fled, the United Nations says.

The invasion, ordered by Russian President Vladimir Putin, has drawn condemnation around the world and increasingly severe economic sanctions against Russia.

With NATO forces massing in the region around Ukraine, various countries have also pledged aid or military support to the resistance. Ukrainian President Volodymyr Zelenskyy called for peace talks — so far unsuccessful — while urging his country to fight back.

Putin insists Ukraine has historic ties to Russia and he is acting in the best security interests of his country. Zelenskyy vowed not to bend.

"Nobody is going to break us, we're strong, we're Ukrainians," he told the European Union in a speech in the early days of the fighting, adding, "Life will win over death. And light will win over darkness."

The Russian attack on Ukraine is an evolving story, with information changing quickly. Follow PEOPLE's complete coverage of the war here, including stories from citizens on the ground and ways to help.