Evidence from Mariupol indicates "serious" and "gross violations" of international humanitarian and humans rights laws occurred during the battle for the city and the remaining residents now face a "dire" situation, a top UN official warned Thursday.

Driving the news: United Nations High Commissioner for Human Rights Michelle Bachelet told the UN Human Rights Council in Geneva residents have limited access to basic utilities and services including medical care and "risks of infectious disease, including cholera are being reported" in the Russian-occupied port city.

The big picture: Mariupol was "likely the deadliest place in Ukraine" during fighting from February through the end of April, when Russian forces seized control of most of the southern city, Bachelet said in her update on what she called "the grave human rights and humanitarian situation in Mariupol."

• Bachelet noted that the Russian airstrike on the Mariupol theater in March was among "the deadliest and most emblematic examples of the harm caused to civilians."
• "The theatre had hundreds of civilians hiding inside with signs clearly marked 'children,' visible from the sky," she said.

By the numbers: An estimated 350,000 people were forced to flee Mariupol, while UN assessments indicate that up to 90% of the city's residential buildings and up to 60% of private houses have been damaged or destroyed.

Where it stands: "Many people either no longer have a place to live or live in damaged apartments, often with no windows, electricity, gas and running water," Bachelet said.

• "People cannot leave and return to the city freely, including those who left Mariupol in April or March," she continued.
• "I am also concerned about the way the so-called 'filtration' process of civilians was and is being carried out, reportedly involving arbitrary determinations, intimidation and humiliation, which may amount to ill-treatment, as well as reported instances of family separation and threats to the right to private life," Bachelet added.
• "The related risks of detention and ill-treatment for those who do not pass the process are also of concern."

The bottom line: "The tragedy of Mariupol is far from over, and the full picture of the devastation caused is not yet clear," Bachelet said.

What to watch: Bachelet said in April there was growing evidence of war crimes and other human rights violations in Ukraine, and the International Criminal Court and others have opened investigations into such allegations.

Yes, but: War crimes have been historically hard to investigate and often even more challenging to prosecute, per Axios' Laurin-Whitney Gottbrath.

Go deeper: Dashboard: Russian invasion of Ukraine

Editor's note: This article has been updated with further context.