(NewsNation) —  Vice President Kamala Harris Thursday joined international calls for a war crimes investigation of Russia over its invasion of Ukraine and the bombing of civilians, including a maternity hospital.

Harris expressed outrage over the bombing of the maternity hospital and scenes of bloodied pregnant women being evacuated, saying, “We should all be watching.”

Ukrainian President Volodymyr Zelenskyy has also repeatedly called the invasion of Ukraine a war crime.

The International Criminal Court’s chief prosecutor said last week he plans to open an investigation “as rapidly as possible” into possible war crimes and crimes against humanity in Ukraine — both alleged crimes committed before the Russian invasion, but also any new crimes that either side might have committed since the invasion started.

War crimes, as defined in the aftermath of World War II include: willfully killing, torture, extensive destruction not justified by military means, compelling a prisoner of war to serve in its enemy’s army and hostage-taking.

Proving intent to commit a war crime can be extremely difficult. Since the court’s founding, 45 individuals have been prosecuted for committing war crimes or crimes against humanity.

Russia is specifically accused of targeting civilian populations, which is not justified by military means, like the maternity hospital in Mariupol and Freedom Square in Kharkiv.

Essentially, ICC is the only one in the world that can prosecute individuals for committing atrocities or crimes of aggression when that person’s own country won’t or is incapable of doing so.

The court can also investigate genocide or crimes of aggression (ex, one state antagonizing another state).

Both Russia and Ukraine are not officially members of the ICC. But Ukraine accepted its jurisdiction so ICC can pursue a case. In fact, the ICC already had an open case from 2014 that found significant evidence war crimes were committed during Russia’s invasion of Crimea.

The court paused the investigation in 2020 due to a lack of resources.

Harris’s and Zelenskyy’s comments come after a NewsNation/Decision Desk HQ poll that found there is broad support for continuing to arm the Ukrainians in their fight against Russia as well as for the economic sanctions imposed by the United States. But Americans draw a line: They are almost as strongly against using U.S. troops to defend Ukraine.

You can read the full poll results here.