The Russian Federation should immediately cease military actions in Ukraine, which began on February 24, "judge Joan Donoghue informed the International Court of Justice.
"The court is deeply worried by the Russian Federation's use of force, which poses major questions in international law," Donoghue said in The Hague.
On February 27, Ukraine filed an urgent complaint with the ICJ stating that Russia had justified its war by claiming genocide in the Donetsk and Lugansk areas.
Ukraine has urged the court to provisionally stop the invasion while it awaits a final decision that could take years.
Experts say a favourable verdict for Ukraine would help raise its profile globally.