Kamala Harris was speaking at a security conference, where leaders called for long-term support of Ukraine.
The US has “formally determined” that Russia has committed crimes against humanity in Ukraine, US Vice-President Kamala Harris has said.
Speaking at the Munich Security Conference, Ms Harris accused Russia of “gruesome acts of murder, torture, rape and deportation” since its invasion.
Russian perpetrators “will be held to account”, she added.
The UN defines such crimes as part a “widespread or systemic attack” on a particular civilian population.
Moscow has repeatedly denied targeting civilians during its invasion.
“In the case of Russia’s actions in Ukraine we have examined the evidence, we know the legal standards, and there is no doubt: these are crimes against humanity,” Ms Harris, a former prosecutor, told the conference.
She cited “barbaric and inhumane” atrocities during the war in Ukraine, including the scores of bodies found in Bucha shortly after the invasion and the bombing of a theatre in Mariupol.
“Let us all agree: on behalf of all the victims, both known and unknown, justice must be served,” Ms Harris said.
The official determination that Moscow is carrying out crimes against humanity came at the end of a legal analysis led by the US State Department.
The US government had already accused Moscow of war crimes, but calling them crimes against humanity means that acts from murder to rape are widespread, systematic and intentionally directed against civilians. It is considered more serious under international law.
There are 15 crimes that count as a crime against humanity – among them murder, enslavement, torture, rape and deportation.
Crimes against humanity are tried at the International Criminal Court (ICC).
But the ICC has no powers to arrest suspects and can only exercise jurisdiction within countries which signed up to the agreement that set up the court.
Russia is not a signatory to that agreement, so it is unlikely to extradite any suspects.
World leaders are meeting in Munich as the one-year anniversary of Russia’s full-scale invasion of Ukraine approaches on 24 February.
UK Prime Minister Rishi Sunak called on Western allies to “double down” on their support for Ukraine and help guarantee Kyiv’s long-term security.
Mr Sunak told the conference that allies must give the country “advanced, Nato-standard capabilities”.
The three-day gathering will provide a key test of Western support for Kyiv as both sides in the war prepare for spring offensives.
Ukraine’s Foreign Minister Dmytro Kuleba said Moscow had “waged a genocidal war” because it did not think Ukrainians “deserve to exist as a sovereign nation”.
Tens of thousands have lost their lives and millions have been forced from their homes as part of Vladimir Putin’s invasion.