Russia declined to attend a hearing at the UN's top court on Monday at which Ukraine is asking for an immediate order to halt the conflict, the head judge said.
"The court regrets the non-appearance of the Russian Federation in these oral proceedings," International Court of Justice President Joan Donoghue said.
The Russian ambassador to the Netherlands, Alexander Shulgin, wrote to the court and "indicated that his government did not intend to participate," she said.
Ukraine's representative at the court in The Hague, Anton Korynevych, criticised Russia for not showing up at the ICJ's Peace Palace headquarters.
"The fact that Russia's seats are empty speaks loudly. They are not here in this court of law, they are on a battlefield, waging aggressive war against my country," he said.
"This is how Russia solves disputes."
Kyiv lodged an urgent case at the ICJ on February 27, saying that Russia had illegally justified its war by falsely alleging genocide in Ukraine's Donetsk and Lugansk regions.
Ukraine has asked the court to take provisional measures ordering Russia to "immediately suspend the military operations", pending a full judgment that could take years.
Korynevych added that the court "has a responsibility to act."
"Russia must be stopped, and the court has a role to play in stopping that," he said.
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