The disturbing details and images of the death of a six-year-old Ukrainian girl in a shelling attack on Mariupol is the latest incident to highlight the human cost of the conflict in Ukraine. 

Ukrainian photo-journalist, Mstyslav Chernov, working for U.S. news agency the Associated Press, detailed the desperate attempts of surgeons to save her life.

"She was pale. Her brown hair was pulled back with a rubber band. Her bloody pyjama pants were decorated with cartoon unicorns," Chernov said. "She was brought in with her wounded father, his head bloodied and bandaged. A medical team pumped her chest, fighting desperately to revive her. Her mother stood outside the ambulance, weeping."

Russian forces currently attacking the port city have been accused of war crimes by Ukraine, which says civilians have been targeted. Russia says its troops are there to protect people from the government in Kyiv which it accuses of human rights abuses against its own people.

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Chernov described how a hospital worker wheeled a gurney to the ambulance, shouting, "Take her out, take her out. We can make it." The girl was raced inside and doctors and nurses huddled around her, immediately administering an injection as other staff attempted to revive her with a defibrillator. 

One nurse wept as a doctor in blue medical scrubs, pumping oxygen into the girl. Despite the medical staff's efforts, the girl, whose name was not immediately known, could not be saved. The doctor reached gently over her face to close her eyes. Her body was left alone in the room, covered by her brightly colored polyester jacket, now spattered with blood.

The exact number of children killed in the invasion is unknown. The UN announced that at least 136 civilians had lost their lives, including 13 children, and over 400 have been injured. 

"The real toll is likely to be much higher," Liz Throssell, a spokesperson for the UN Human Rights Council told a briefing, adding that almost half of the casualties were in the Donetsk and Luhansk regions in eastern Ukraine.

Authorities in two Russian-backed breakaway republics in the east say civilian infrastructure in their areas has been hit by Ukrainian shelling.

In Ukraine's capital Kyiv, the city's deputy mayor, Vladimir Bondarenko, shared an image of a 10-year-old girl called Polina, who was reportedly shot dead while trying to flee the capital. 

The war is increasingly being fought in and around cities as Russia advances on the major urban areas of Kyiv, Kharkiv and Mariupol, among others. Although many have fled the violence, civilians are still being killed. The ones that make it to the relative safety of the border are still scarred by what they've seen. "I saw war, I saw rockets," 15-year-old Ivan told a Reuters reporter on the Hungarian border.