The UN's highest court, the International Court of Justice (ICJ), ruled on an urgent request by Ukraine for Russia to halt its invasion.
The 13-2 verdict called for the Russian Federation to immediately suspend the military operations that it commenced on February 24. Only Russian and Chinese judges dissented, according to reports.
The ruling is the first such verdict handed by an international court since the war in Ukraine began.
Ukrainian President Volodymyr Zelenskyy welcomed the news on Twitter, saying that "Ukraine gained a complete victory in its case against Russia at the International Court of Justice. The ICJ ordered to immediately stop the invasion. The order is binding under international law. Russia must comply immediately. Ignoring the order will isolate Russia even further."
What is the case?
Kyiv accuses Moscow of illegally trying to justify the war by falsely claiming genocide in eastern Ukraine's Donetsk and Luhansk regions.
Ukraine's representative Anton Korynevych sought to get the ICJ to order Russia to "immediately suspend the military operations."
"Russia must be stopped, and the court has a role to play," Ukraine's representative Anton Korynevych told the court, which is based in The Hague.
Russia boycotted the ICJ's hearings earlier this month.
In a written filing, Moscow argued that the court "did not have jurisdiction" because Ukraine's request fell outside of the scope of the UN's 1948 Genocide Convention upon which it based its case.
Russia went on to say "it was acting in self-defense" to justify its invasion of Ukraine.
Ukraine said the Genocide Convention, which both countries have signed, does not allow an invasion to prevent a genocide. There is no evidence of Ukraine committing or planning attacks that could be deemed crimes against humanity.
Does the case fall under the ICJ's jurisdiction?
The ICJ ruled that Ukraine's request fell under the court's jurisdiction.
The ICJ was set up after the World War II to rule on disputes between UN member states, based mainly on treaties and conventions.
The ICJ's rulings are binding, but it has no executive means to enforce them in countries.
The case is separate from a war crimes investigation in Ukraine launched by the International Criminal Court (ICC), a separate tribunal also based in The Hague.
What are the latest developments in Ukraine?
Wednesday's ICJ session comes as Russian forces step up strikes on residential buildings in Kyiv.
The number of refugees fleeing Ukraine has topped 3 million, according to the refugee agency UNHCR.
The UN human rights office reported that 691 people have been killed and 1,143 injured so far, noting that the actual figures were likely "considerably higher."
Meanwhile, Ukraine's President Zelenskyy said that the positions in the negotiations between Russian and Ukrainian representatives were starting to sound "more realistic." On Wednesday, Russian Foreign Minister Sergey Lavrov said there is "hope for compromise."