U.N. investigators say they've recorded nearly 3,000 civilian deaths in Ukraine.

Russia has been accused of committing war crimes there and some world leaders, including President Biden and Ukraine's Volodymyr Zelenskyy, have accused Russia of genocide. Since the war began, international groups have been working to document the carnage.

"Unfortunately, the longer this conflict goes on, the more violations we're finding," says Matilda Bogner, the head of a U.N. team of investigators documenting possible human rights abuses in Ukraine.

Morning Edition spoke with Bogner about what her team has seen in Ukraine. Listen here.

Bogner reports her team has investigated Russia's indiscriminate use of weapons with wide explosive impact in civilian-populated areas, cases where civilians have been unlawfully killed in summary executions and the use of sexual violence, as well as other possible violations of human rights.

"There are high numbers of allegations of sexual violence," in the areas around Kyiv that Russian forces controlled, reports Bogner. "But there are allegations in other parts of the country too, and by both sides in the conflict."

It can be difficult to prosecute genocide and other war crimes in international courts and it is unclear yet where war crimes committed in Ukraine could ultimately be prosecuted. Neither Ukraine nor Russia nor the U.S. is a party to the International Criminal Court, which has prosecuted war crimes in other regions and conflicts.

"But at this stage, what is important is to ensure that the crimes are being documented," says Bogner. "So when opportunities arise in the future, then they can be prosecuted."

Continue below for more of their conversation, which was edited lightly for length and clarity.

On the use of sexual violence during the war:

We have also been looking at sexual violence. We have dozens of allegations. We have been able to confirm some of them. It is difficult to fully confirm sexual violence because it's often the type of case where victims don't want to speak publicly, and they're often not in safe areas where it feels safe for them to speak out, or where they have received the services that they need. So it's difficult, but we are particularly concerned [with] the areas around Kyiv where Russian forces were and then left. There are high numbers of allegations of sexual violence in those areas, but there are allegations in other parts of the country too, and by both sides in the conflict, unfortunately.

On the nature of the crimes her team is investigating:

We've been speaking to people who have been able to evacuate from Mariupol, and we've been hearing a lot of awful stories from them. One story was from a medical doctor who remained to work in the hospital, and he said that more than 90 percent of the patients that he was so-called treating, it was by telephone, because they could not reach him. It was too dangerous for them to get to him. People have been stuck in basements, without food, without water.

If what her team is seeing could be evidence of genocide:

So far, what we've been documenting is individual violations of international human rights law, as well as violations of international humanitarian law, which may constitute war crimes. So far, we have not looked into the question of genocide in Ukraine. We have enough to try to document these individual cases. I think it will be something for the courts to look at at a later stage.

On how war crimes are prosecuted under international law:

There are different levels at which people can be prosecuted. Certainly, the government of Ukraine has already opened cases. Other countries can also look at that. Some of these crimes have universal jurisdiction, so different countries could also prosecute. But then there are regional courts. There's the European Court of Human Rights and the international courts, such as the International Criminal Court. It's a pity neither Russia nor Ukraine are parties to the ICC. However, Ukraine has given permission for the ICC to look into conflict-related issues within its territory that happened before the 24th of February, when this international armed conflict started. But it can apply to this also, so the ICC is looking into what is happening in Ukraine at the moment. But at this stage, what is important is to ensure that the crimes are being documented. So when opportunities arise in the future, then they can be prosecuted.

This story first appeared on the Morning Edition live blog.

Copyright 2022 NPR. To see more, visit https://www.npr.org.