The International Criminal Court has issued an arrest warrant for Russian president Vladimir Putin and another senior Russian official accused of war crimes.

It’s a historic move that heightens international tensions and takes the battle from the ground to the court room. And it marks the first time a leader of a country with a permanent seat on the UN Security Council has ever been called for trial before the UN court.

The warrants concern Russia’s forced deportation of children from Russian-occupied areas of Ukraine. The court said in a statement, “There are reasonable grounds to believe that Mr. Putin bears individual criminal responsibility.”

Moscow rebuffed the court’s warrant, with Foreign Ministry spokeswoman Maria Zakharova saying that the court’s warrant is “of no importance for our country.”